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                                                                     Exhibit 3.4

                            CERTIFICATE OF AMENDMENT
                                       OF
                           CERTIFICATE OF DESIGNATION
                                       OF
                                  US LEC CORP.

      US LEC Corp., a Delaware corporation (the "Corporation") hereby executes
and certifies this Certificate of Amendment for the purposes of amending its
Certificate of Designation relating to its Series A Convertible Preferred Stock,
filed with the office of the Delaware Secretary of State on April 11, 2000,
under the General Corporation Law of the State of Delaware:

      1.    The name of the corporation is US LEC Corp.

      2.    A majority of the Corporation's Series A Preferred Stockholders
            approved the following amendment to the Corporation's Certificate of
            Designation as of the 6th day of August, 2001, in the manner
            prescribed by law, for the purpose of amending the definition of
            "Change of Control" contained in ARTICLE 11 of the Certificate of
            Designation, so that, as amended, clause such definition shall be
            and read as follows:

                  "Change of Control" means (i) the failure of Richard T. Aab
                  ("Aab") and Tansukh V. Ganatra ("Ganatra"), in the aggregate,
                  to own or control, directly or indirectly, stock of the
                  Corporation representing at least 50% of the total number of
                  shares of voting capital stock of the Corporation (as adjusted
                  for the events described in Section 4.3) that they, in the
                  aggregate, own or control, directly or indirectly, as of the
                  Initial Issue Date after reducing the number of such shares as
                  of the Initial Issue Date by 2.0 million, (ii) the failure of
                  Aab and Ganatra, in the aggregate, to own or control, directly
                  or indirectly, more shares of the voting capital stock of the
                  Corporation than any other Person or group (other than a
                  Permitted Owner or group of the Permitted Owners and their
                  Affiliates), within the meaning of Regulation 13D under the
                  Securities Exchange Act of 1934 or (iii) a Change of Board
                  shall occur; provided, however, that if, upon the simultaneous
                  death of Aab and Ganatra or upon the death of the last to
                  survive of Aab and Ganatra, all of the Class A Common Stock
                  owned or controlled, directly or indirectly, by Aab and
                  Ganatra is held by Permitted Transferees (as defined in the
                  Certificate of Incorporation) of Aab and Ganatra, such Class A
                  Common Stock shall be deemed to be controlled by Aab and
                  Ganatra for purposes of clauses (i) and (ii) so long as such
                  Class A Common Stock is held by such Permitted Transferees.

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      In all other respects, Article 11 and all other provisions of the
Certificate of Designation shall remain the same.

      3. The foregoing amendment to the Certificate of Designation herein
certified was duly adopted in accordance with the applicable provisions of
Sections 228 and 242 of the General Corporation Law of the State of Delaware.

      Signed on the 6th day of August, 2001.

                                    US LEC CORP.


                                    By: /s/ Michael K. Robinson
                                        ----------------------------------------
                                            Michael K. Robinson
                                            Executive Vice President
                                            and Chief Financial Officer