<PAGE>

                                                                 Exhibit 10.15.2

                   FIRST AMENDMENT TO STOCKHOLDERS' AGREEMENT

          THIS FIRST AMENDMENT TO STOCKHOLDERS' AGREEMENT (this "Amendment") is
made as of this 4th day of February 2000 by and among PaeTec Corp., a Delaware
corporation (the "Corporation"), Alliance Cabletel Holdings, L.P., a Delaware
limited partnership ("Alliance"), Kline Hawkes California SBIC, L.P. ("Kline
Hawkes"), The Union Labor Life Insurance Company Separate Account P ("ULLICO"),
the individuals listed on the signature pages hereto (together with Alliance,
Kline Hawkes and ULLICO, the "CCS Group Stockholders"), Arunas A. Chesonis ("Mr.
Chesonis"), Christopher E. Edgecomb, ("Mr. Edgecomb"), Trustee of the
Christopher E. Edgecomb Living Trust dated April 25, 1998 (the "Trust"), and
Jeffrey Sudikoff ("Mr. Sudikoff," and together with Mr. Chesonis and Mr.
Edgecomb, the "Majority Stockholders").  The CCS Group Stockholders and the
Majority Stockholders are hereinafter sometimes collectively referred to as the
"Stockholders" and individually as a "Stockholder."

                                    RECITALS
                                    --------

     A.  The Corporation and the Stockholders are parties to a Stockholders'
Agreement dated as of September 9, 1999 (the "Stockholders' Agreement").

     B.  Section 2 of the Stockholders' Agreement grants to each of the CCS
Group Stockholders tag-along rights in the event that one or more of the
Majority Stockholders proposes to transfer any Securities (as defined in the
Stockholders' Agreement) and according to the terms and conditions of the
Stockholders' Agreement.

     C.  Section 3 of the Stockholders' Agreement provides that each CCS Group
Stockholder shall have a preemptive right to acquire capital stock of the
Corporation in certain circumstances specified therein.

     D.  The Board of Directors of the Corporation has authorized the issuance
and sale (the "Series A Preferred Stock Placement") of up to 134,000 shares of a
new series of preferred stock of the Corporation, designated the Series A
Convertible Preferred Stock (the "Series A Preferred Stock"), to the purchasers
(the "Purchasers") listed on the Schedule of Purchasers to, and pursuant to the
terms and conditions of, an Equity Purchase Agreement (the "Purchase
Agreement").

     E.  As a condition to the consummation of the Series A Preferred Stock
Placement, the Purchasers have required that the Corporation, the Majority
Stockholders and the Purchasers enter into a Stockholders' Agreement (the
"Stockholders' Agreement of the Purchasers"), dated the date of the Purchase
<PAGE>

Agreement, pursuant to which the Purchasers will be entitled to certain tag-
along rights (the "Purchasers' Tag-Along Rights") in the event that one or more
of the Majority Stockholders proposes to transfer certain securities of the
Corporation.

     F.  As a condition to the consummation of the Series A Preferred Stock
Placement, the Purchasers have required that the parties hereto enter into a
Voting Agreement (the "Voting Agreement"), with the Purchasers which, among
other things, will replace and supersede Section 4 of the Stockholders'
Agreement to the extent the terms of such Section 4 conflict with or are
inconsistent with the terms of the Voting Agreement.

     G.  The parties hereto desire to amend the Stockholders' Agreement to
induce the Purchasers to consummate the Series A Preferred Stock Placement.


                                   AGREEMENT
                                   ---------

          1.  Defined Terms.  All capitalized terms used in this Amendment
              -------------
without definition shall have the meanings given to such terms in the
Stockholders' Agreement.  All capitalized terms defined in this Amendment,
including the recitals hereof, and not defined in the Stockholders' Agreement
are hereby incorporated into and made a part of the Stockholders' Agreement, as
amended by this Amendment.

          2.  Amendment of Section 2.1.  Section 2.1 of the Stockholders'
              ------------------------
Agreement is hereby amended, replaced and superseded to read in its entirety as
follows:

          "2.1  Right to Transfer.  If, at any time, one or more of the
                -----------------
     Majority Stockholders (which term, for purposes of this Section 2 shall
     refer to such Majority Stockholders and/or each of the Permitted
     Transferees of such Majority Stockholders) propose to Transfer any class or
     type of Securities to any Person (other than a Transfer to a Permitted
     Transferee), such Majority Stockholder (a "Transferring Stockholder") shall
     give written notice to each of the CCS Group Stockholders (which term, for
     the purposes of this Section 2 shall refer to such CCS Group Stockholder
     and/or each of the Permitted Transferees of such CCS Group
     Stockholders)("Non-Transferring Stockholders") and the Corporation at least
     25 business days prior to the consummation of the proposed Transfer (the
     "Tag-Along Notice").  Each Non-Transferring Stockholder holding such class
     or type of Securities may, upon giving written notice to the Transferring
     Stockholder and the Corporation within 15 business days after its receipt
     of the Tag-Along Notice (a "Tag-Along Election Notice"), participate in
     such Transfer on a pro rata basis, at the same price and
                        --- ----

                                      -2-
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     upon the same terms and conditions as are applicable to the Transferring
     Stockholder in such transaction. For purposes of the preceding sentence,
     each Non-Transferring Stockholder's pro rata share shall be a percentage of
                                         --------
     the total number of such type or class of Securities that the purchaser
     agrees to purchase, such percentage to be determined by dividing (a) the
     number of Securities of such type or class that such Non-Transferring
     Stockholder submits for sale pursuant to Section 2.2, by (b) the number of
     Securities of such type or class proposed to be sold by the Transferring
     Stockholder plus the total number of Securities of such type or class that
                 ----
     all Non-Transferring Stockholders submit for sale pursuant Section 2.2 plus
                                                                            ----
     the total number of Securities of such type or class that the Purchasers
     have the right to Transfer in such transaction pursuant to Section 2.2 of
     the Stockholders' Agreement of the Purchasers, plus, with respect to a
                                                    ----
     proposed Transfer by Mr. Chesonis, the total number of Securities of such
     type or class that (i) Mr. Edgecomb and Mr. Sudikoff have the right to
     Transfer in such transaction pursuant to Section 3 of the Majority
     Stockholders' Agreement and (ii) certain officers of the Corporation have
     the right to Transfer in such transaction pursuant to the Stock Right
     Agreements."

          3.    Amendment of Section 2.6.  Section 2.6 of the Stockholders'
                ------------------------
Agreement is hereby amended, replaced and superseded to read in its entirety as
follows:

                "2.6 No Other Tag-Along Rights. Except for (i) the rights
                     -------------------------
     granted to the Purchasers under Section 2 of the Stockholders' Agreement of
     the Purchasers, (ii) the co-sale rights granted to Mr. Edgecomb and Mr.
     Sudikoff under the Majority Stockholders' Agreement, (iii) the co-sale
     rights granted under the Stock Rights Agreements, and (iv) the rights
     granted to the CCS Group Stockholders under Section 2 of this Agreement, no
     Majority Stockholder shall grant tag-along, co-sale or other rights similar
     to the rights granted to the CCS Group Stockholders under this Section 2
     (i.e., the right to participate in the Transfer of Securities in connection
      ----
     with a Transfer of Securities by a Principal Stockholder) without the prior
     written consent of CCS Group Stockholders holding a majority of the shares
     of Common Stock held by all CCS Group Stockholders on the applicable date
     that such Majority Stockholder desires to grant such rights."

          4.    Amendment of Section 3.1. Section 3.1 of the Stockholders'
                ------------------------
Agreement is hereby amended, replaced and superseded to read in its entirety as
follows:

                                      -3-
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          "3.1 Right to Purchase.  Subject to Section 3.3, each CCS Group
               -----------------
     Stockholder (which term, for purposes of this Section 3 shall refer to (i)
     each CCS Group Stockholder, (ii) each of the Permitted Transferees of each
     CCS Group Stockholder, and (iii) each third party transferee of Securities
     from a CCS Group Stockholder who is entitled to enjoy the rights of such
     CCS Group Stockholder hereunder pursuant to Section 8.5 of this Agreement)
     shall have a preemptive right to acquire any shares of any class of capital
     stock of the Corporation, including unissued shares, treasury shares or any
     rights or options to purchase such capital stock, or any securities
     convertible into or exchangeable for such capital stock or any options to
     purchase such convertible or exchangeable securities (collectively,
     "Capital Stock"), authorized by the Board of Directors of the Corporation
     for issuance after the date hereof.  Such preemptive right shall entitle
     each CCS Group Stockholder to purchase up to such CCS Group Stockholder's
     pro rata share of all Capital Stock on a fully diluted basis assuming the
     --- ----
     exercise of all outstanding options, warrants and conversion rights to
     purchase or acquire Capital Stock, based on such CCS Group Stockholder's
     actual and assumed holdings at that date, at the same price and on the same
     terms and conditions as those upon which such Capital Stock is proposed to
     be sold.  Notwithstanding the foregoing, such preemptive right shall not
     apply to any such Capital Stock (each an "Excluded Issuance"): (a) issued
     in the Series A Preferred Stock Placement pursuant to the Purchase
     Agreement; (b) issued upon conversion of the Series A Preferred Stock in
     accordance with the terms of the Corporation's certificate of
     incorporation; (c) issued upon the exercise of the warrants and options
     outstanding as of February 4, 2000 (as set forth on the Capitalization
     Schedule attached to the Purchase Agreement) or warrants or options granted
     or Common Stock issued by the Corporation pursuant to the Corporation's
     1998 Incentive Compensation Plan or PaeTec Communications, Inc. Agent
     Incentive Plan without any increase in the number of shares of Capital
     Stock issuable under such plans (other than increases caused by stock
     splits and similar recapitalizations) from the number of shares of Capital
     Stock set forth in Section 5 of the Purchase Agreement; (d) issued as a
     dividend or other distribution on Capital Stock; (e) issued in connection
     with a merger or consolidation permitted under or approved pursuant to
     Section 5.1(g) of this Agreement; (f) issued upon the exchange, conversion
     or exercise of any Securities that are exchangeable for, convertible into
     or exercisable for shares of Capital Stock, the original issuance of which
     was authorized in compliance with Section 5.1 of this Agreement; or (g)
     issued to the public in connection with an initial

                                      -4-
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     public offering of the Corporation's Common Stock with gross proceeds in
     excess of $25 million."

          5.  Application of Section 4.
              ------------------------

          (a) The provisions of Section 4 of the Stockholders' Agreement, as
modified by Section 5(b) of this Amendment, shall continue in full force and
effect to the extent, but only to the extent, that the provisions of such
Section 4 do not conflict with and are not inconsistent with the provisions of
the Voting Agreement.  To the extent that the provisions of such Section 4
conflict with or are inconsistent with any provisions of the Voting Agreement,
the provisions of the Voting Agreement shall control.

          (b)  Section 4.2 of the Stockholders' Agreement is hereby amended,
replaced and superseded to read in its entirety as follows:

              "4.2  Termination. The provisions set forth in this Section 4
                    -----------
          shall terminate on the date that the CCS Group Stockholders (including
          their Permitted Transferees) cease to own, on an aggregate basis, at
          least 5% of the issued and outstanding shares of Common Stock of the
          Corporation."

          6.  Amendment of Section 5.1(a). Section 5.1(a) of the Stockholders'
              ---------------------------
Agreement is hereby amended, replaced and superseded to read in its entirety as
follows:

          "(a)  any acquisitions of assets for consideration in excess of (i)
     $10 million in any single transaction or series of related transactions or
     (ii) $50 million in the aggregate;"

          7.  Waiver of Rights; Consent.  The CCS Group Stockholders hereby
              -------------------------
waive any rights they may have under the Stockholders' Agreement (whether
pursuant to Section 3 thereunder or otherwise) and under any other agreement to
participate in the purchase and sale of the Series A Preferred Stock under the
Purchase Agreement (including with respect to any shares of Common Stock or
other securities issued upon conversion of such Series A Preferred Stock) and
any other rights they have with respect to such purchase and sale, and hereby
consent to the consummation of the purchase and sale of the Series A Preferred
Stock and the other transactions contemplated by the Purchase Agreement.

          8.  Binding Effect.  This Amendment shall be binding upon and inure to
              --------------
the benefit of the parties hereto and their heirs, executors, administrators,
successors and assigns.

                                      -5-
<PAGE>

          9.  Governing Law.  This Amendment shall be governed by, and construed
              -------------
and enforced in accordance with, the laws of the State of New York, except that
if any provision of this Amendment or any part of any such provision would be
illegal, invalid or enforceable under such laws in connection with a suit or
proceeding validly instituted in another jurisdiction, then the laws of such
other jurisdiction shall govern insofar as is necessary to sustain the legality,
validity or enforceability of such provision or any part of such provision.

          10.  Captions.  Captions to the Sections in this Amendment are for the
               --------
convenience of the parties only and shall not affect the meaning or
interpretation of this Amendment.

          11.  Enforceability and Interpretation.  It is the intention of the
               ---------------------------------
parties to this Amendment that the terms and provisions contained in this
Amendment shall be enforceable to the fullest extent permitted by law.  If any
term or provision of this Amendment or the application thereof to any Person or
circumstance is construed to be illegal, invalid or unenforceable, in whole or
in part, then such term or provision shall be construed in such a manner as to
permit its enforceability under applicable law to the fullest extent permitted
by such law.  In any case, the remaining terms and provisions of this Amendment
or the application thereof to any Person or circumstance, except those terms and
provisions which have been held illegal, invalid or unenforceable, shall remain
in full force and effect.

          12.  Counterparts.  This Amendment may be executed in one or more
               ------------
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

          13.  Additional Documents.  Each party hereto agrees to execute any
               --------------------
and all documents, instruments, certificates and communications deemed to be
necessary or advisable by the Corporation to effectuate the purposes of this
Amendment.

                            [signature pages follow]

                                      -6-
<PAGE>

          IN WITNESS WHEREOF, the parties hereto have executed and delivered
this Amendment with full force and effect as of the day and year first written
above.

                            THE CORPORATION:

                            PAETEC CORP.


                            By: /s/ Arunas A. Chesonis
                               ------------------------------
                            Its:  CEO, Chairman and President


                            MAJORITY STOCKHOLDERS PARTY
                            HERETO:

                            /s/ Arunas A. Chesonis
                            ---------------------------------
                            Arunas A. Chesonis


                            /s/ Jeffrey Sudikoff
                            ---------------------------------
                            Jeffrey Sudikoff

                            /s/ Christopher E. Edgecomb
                            ---------------------------------
                            Christopher Edgecomb, Trustee of the
                            Christopher E. Edgecomb Living Trust dated
                            April 25, 1998

                            CCS GROUP STOCKHOLDERS:

                            ALLIANCE CABLETEL HOLDINGS, L.P., a
                            Delaware limited partnership


                            By:  KOCOM COMMUNICATIONS, INC., a
                                 Delaware limited partnership


                            By: /s/ James A. Kofalt
                                -----------------------------
                                James A. Kofalt, President

                                      -7-
<PAGE>

                            KLINE HAWKES CALIFORNIA SBIC, L.P.


                            By:    /s/ Frank Kline
                            ----------------------------
                            Its:  Chairman


                            THE UNION LABOR LIFE INSURANCE
                            COMPANY SEPARATE ACCOUNT P


                            By:    /s/ Joseph Linehan
                            ----------------------------
                            Its:  VP - Securities



                                  /s/ Robert I. Schwartz
                            ----------------------------
                            Robert I. Schwartz


                                  /s/ Kenneth M. Kiraly
                            ----------------------------
                            Kenneth M. Kiraly


                                  /s/ Susan F. Kiraly
                            ----------------------------
                            Susan F. Kiraly


                                  /s/ Richard P. Rizzutti
                            ----------------------------
                            Richard P. Rizzutti


                                  /s/ Bryant Hopper
                            ----------------------------
                            Bryant Hopper


                                  /s/ Ronald S. Johnson
                            ----------------------------
                            Ronald S. Johnson


                                     -8-
<PAGE>

                                  /s/ Lodwrick Cook
                            ------------------------------
                            Lodwrick Cook


                                  /s/ Peter Cracovaner
                            ------------------------------
                            Peter Cracovaner


                                  /s/ Richard Cunningham
                            ------------------------------
                            Richard Cunningham

                                  /s/ Thomas O. Fitzgerald
                            ------------------------------
                            Thomas O. Fitzgerald


                                  /s/ Wendy Foliano
                            ------------------------------
                            Wendy Foliano


                                  /s/ Joseph Golden
                            ------------------------------
                            Joseph Golden


                                  /s/ Stephen Mayo
                            ------------------------------
                            Stephen Mayo


                                  /s/ Karen Sancimino
                            ------------------------------
                            Karen Sancimino


                                  /s/ Clint Walker
                            ------------------------------
                            Clint Walker

                                      -9-