<PAGE>

                                                                   EXHIBIT 10.26

                      AMENDMENT NO. 1 TO CREDIT AGREEMENT
                      -----------------------------------


          THIS AMENDMENT NO. 1 TO CREDIT AGREEMENT (this "Amendment") effective
                                                          ---------
as of March 20, 2001, by and among GLOBAL PAYMENTS INC., a Georgia corporation,
as Borrower, the banks and other financial institutions listed on the signature
pages hereof, as Lenders, BANK ONE, NA, a national banking association having
its principal office in Chicago, Illinois, as Administrative Agent, Swing Line
Lender and LC Issuer, SUNTRUST BANK, a Georgia banking corporation, as
Documentation Agent, and WACHOVIA BANK, N.A., a national banking association, as
Syndication Agent.

                              W I T N E S S E T H:
                              - - - - - - - - - -

          WHEREAS, Borrower, the Lenders, and the Agents are parties to a
certain Credit Agreement dated as of January 31, 2001 (the "Credit Agreement";
capitalized terms used in this Amendment without definition that are defined in
the Credit Agreement shall have the meanings in this Amendment as specified for
such capitalized terms in the Credit Agreement);

          WHEREAS, Borrower and Lenders constituting the "required lenders"
under the Credit Agreement have agreed to amend the Credit Agreement in certain
respects as set forth in this Amendment;

          NOW, THEREFORE, for and in consideration of the mutual covenants
contained herein and other valuable consideration, the receipt and sufficiency
of which are hereby acknowledged, the parties hereto, intending to be legally
bound, agree as follows:

          SECTION 1.  Amendments to Credit Agreement. Subject to the
                      ------------------------------
satisfaction of the conditions precedent set forth in Section 2 hereof, and
effective as of the Effective Date (as hereinafter defined), the Credit
Agreement is hereby amended as follows:

          1.1  Section 1.1 of the Credit Agreement is hereby amended by adding
               -----------
the new defined terms "CIBC/NDPS Acquisition Note", "GP Canada", and "NDPS/GP
                       --------------------------    ---------        -------
Canada Acquisition Note" and accompanying definitions, in appropriate
-----------------------
alphabetical order, as follows:

          "CIBC/NDPS Acquisition Note" means the promissory note made by NDPS
           --------------------------
     payable to the Canadian Seller in the approximate principal sum of U.S.
     $136,850,000 and given in consideration for the Canadian Acquisition, which
     promissory note shall be repayable in full not later than the next Business
     Day immediately following the execution and delivery of such promissory
     note at the time the Canadian Acquisition is consummated.

          "GP Canada" means Global Payments Canada, Inc., an Ontario
           ---------
     corporation, and its successors and permitted assigns.
<PAGE>

          "NDPS/GP Canada Acquisition Note" means the promissory note made by GP
           -------------------------------
     Canada payable to NDPS in the approximate principal sum of Can. $13,026,960
     and given in partial consideration of the sale and transfer by NDPS to GP
     Canada of the merchant credit card terminals and related tangible property
     of the terminal business acquired by NDPS in the Canadian Acquisition,
     which promissory note shall be repayable on demand with interest payable
     monthly.

          1.2    Section 6.5 of the Credit Agreement is hereby amended by
                 -----------
deleting clause (iii) of said Section 6.5 in its entirety and substituting in
lieu thereof the following clause (iii):

          (iii)  loans or advances by the Borrower to its Operating Subsidiaries
     (but excluding GPS or any Subsidiary of GPS) or by such Operating
     Subsidiaries to the Borrower or to any Subsidiary Guarantor,

          1.3    Section 6.6(b) of the Credit Agreement is hereby amended by
                 --------------
deleting clause (iv) of said Section 6.6(b) in its entirety and substituting in
lieu thereof the following clause:

          (iv)   the total amount of cash consideration paid, and Debt assumed
     or otherwise becoming part of Consolidated Total Debt (excluding Debt of
     NDPS arising pursuant to the Canadian Receivables Credit Facility or the
     CIBC/NDPS Acquisition Note), in such acquisition, together with the
     aggregate amount of such cash consideration and Debt in respect of all
     other acquisitions made during the then-current Fiscal Year (or, in the
     case, of the Borrower's 2001 Fiscal Year, the period from the Closing Date
     through the end of such 2001 Fiscal Year) shall not exceed $50,000,000, and

          1.4    Section 6.7 of the Credit Agreement is hereby amended by
                 -----------
deleting clause (c) of said Section 6.7 in its entirety and substituting in lieu
thereof the following clause (c):

          (c)    Debt owing (i) to the Borrower by any of its Operating
     Subsidiaries (other than Subsidiaries that are members of the GPS Group),
     (ii) to NDPS by GP Canada pursuant to the NDPS/GP Canada Acquisition Note
     (so long as such Debt is repaid in accordance with its terms), (iii) to any
     Operating Subsidiary (which shall not include GPS or Subsidiaries or GPS)
     by any Subsidiary Guarantor, and (iv) Debt owing to GPS by any other
     members of the GPS Group, provided, however, that any such Debt pursuant to
     clauses (i) and (iv) shall be payable on demand on a non-subordinated
     basis;

Section 6.7 of the Credit Agreement is hereby further amended by deleting clause
-----------
(g) of said Section 6.7 in its entirety and substituting in lieu thereof the
following clause (g):

          (g)    Debt owing to the Canadian Seller (i) by NDPS pursuant to the
     CIBC/NDPS Acquisition Note, and (ii) by NDPS pursuant to the Canadian
     Receivables Credit Facility in an aggregate amount outstanding at any time
     not to exceed Can. $140,000,000 plus such additional amount as is necessary
     to fund short-term advances during peak generation periods for Canadian
     Receivables, and the Debt arising from the Guarantee of such Debt of NDPS
     described in this clause (ii) by the Borrower and the Subsidiary
     Guarantors, so long as (x) such Debt is secured by no assets of NDPS or any
     other members of the GPI Group other than Canadian Receivables and the
     proceeds

                                      -2-
<PAGE>

     thereof, and (y) the Canadian Receivables Intercreditor Agreement is in
     full force and effect;

          SECTION 2.  Conditions to Effectiveness of Amendment.  This Amendment
                      ----------------------------------------
shall become effective as of the date first above written (the "Effective Date")
                                                                --------------
on the first day when the Administrative Agent shall have received (i) the duly
executed counterparts of this Amendment, as executed on behalf of Lenders
constituting the Required Lenders, and (ii) the duly executed Subsidiary
Guarantee Supplement, Contribution Agreement Supplement, and other documents as
specified in Section 5.3(f) of the Credit Agreement in order for GP Finance,
Inc. to become an additional Subsidiary Guarantor.

          SECTION 3.  Status of Obligations.  Borrower hereby confirms and
                      ---------------------
agrees that all Loans and all other Obligations outstanding under the Credit
Agreement and the other Loan Documents as of the date hereof were duly and
validly created and incurred by Borrower thereunder, that all such outstanding
amounts are owed in accordance with the terms of the Credit Agreement and other
Loan Documents, and that there are no rights of offset, defense, counterclaim,
claim or objection in favor of Borrower arising out of or with respect to any of
the Loans or other Obligations of Borrower to the Agents or the Lenders, and any
such rights of offset, defense, counterclaim, claims or objections have been and
are hereby waived and released by Borrower.

          SECTION 4.  Representations and Warranties of Borrower.  Borrower,
                      ------------------------------------------
without limiting the representations and warranties provided in the Credit
Agreement, represents and warrants to the Lenders and the Agents as follows:

          4.1  The execution, delivery and performance by Borrower of this
Amendment are within Borrower's corporate powers, have been duly authorized by
all necessary corporate action (including any necessary shareholder action) and
do not and will not (a) violate any provision of any law, rule or regulation,
any judgment, order or ruling of any court or governmental agency, the
certificate of incorporation or by-laws of Borrower, or any indenture, agreement
or other instrument to which Borrower is a party or by which Borrower or any of
its properties is bound or (b) be in conflict with, result in a breach of, or
constitute with notice or lapse of time or both a default under any such
indenture, agreement or other instrument.

          4.2  This Amendment constitutes the legal, valid and binding
obligation of Borrower, enforceable against Borrower in accordance with its
terms.

          4.3  After giving effect to this Amendment, no Default or Event of
Default has occurred and is continuing as of the Effective Date.

          SECTION 5.  Survival.  Each of the foregoing representations and
                      --------
warranties shall be made at and as of the Effective Date.  Each of the foregoing
representations and warranties shall constitute a representation and warranty of
Borrower under the Credit Agreement, and it shall be an Event of Default if any
such representation and warranty shall prove to have been incorrect or false in
any material respect at the time when made.  Each of the foregoing
representations and warranties shall survive and not be waived by the execution
and delivery of this Amendment or any investigation by the Lenders or the
Agents.

                                      -3-
<PAGE>

          SECTION 6.  Ratification of Credit Agreement and Loan Documents.
                      ---------------------------------------------------
Except as expressly amended herein, all terms, covenants and conditions of the
Credit Agreement and the other Loan Documents shall remain in full force and
effect, and the parties hereto do expressly ratify and confirm the Credit
Agreement (as amended herein) and the other Loan Documents.  All future
references to the Credit Agreement shall be deemed to refer to the Credit
Agreement as amended hereby.

          SECTION 7.  Indemnity.  In consideration of the amendments agreed to
                      ----------
by the Lenders pursuant to this Amendment, Borrower hereby indemnifies each
Agent, and each Lender, and their respective officers, partners, directors,
employees, representatives and agents from, and hold each of them harmless
against, any and all costs, losses, liabilities, claims, damages or expenses
incurred by any of them (whether or not any of them is designated a party
thereto) (an "Indemnitee") arising out of or by reason of any investigation,
litigation or other proceeding related to this Amendment, the Credit Agreement
or any other Loan Documents or any actual or proposed use of the proceeds of any
of the Loans, including, without limitation, the reasonable fees and
disbursements of counsel incurred in  connection with any such investigation,
litigation or other proceeding; provided, however, Borrower shall not be
obligated to indemnify any Indemnitee for any of the foregoing arising out of
such Indemnitee's gross negligence or willful misconduct.

          SECTION 8.  No Waiver, Etc.  Borrower hereby agrees that nothing
                      ---------------
herein shall constitute a waiver by the Lenders of any Default or Event of
Default, whether known or unknown, which may exist under the Credit Agreement.
Borrower hereby further agrees that no action, inaction or agreement by the
Lenders, including without limitation, any indulgence, waiver, consent or
agreement altering the provisions of the Credit Agreement which may have
occurred with respect to the non-performance of any obligation under the terms
of the Credit Agreement or any portion thereof, or any other matter relating to
the Credit Agreement, shall require or imply any future indulgence, waiver, or
agreement by the Lenders.

          SECTION 9.  Binding Nature.  This Amendment shall be binding upon and
                      --------------
inure to the benefit of the parties hereto, their respective successors,
successors-in-titles, and assigns.

          SECTION 10. Costs and Expenses.  Borrower shall be responsible for
                      ------------------
the costs and expenses of the Agents in connection with the preparation,
execution and delivery of this Amendment and the other instruments and documents
to be delivered hereunder, including, without limitation, the fees and out-of-
pocket expenses of counsel for the Agents with respect thereto.

          SECTION 11. GOVERNING LAW.  THIS AMENDMENT SHALL BE GOVERNED BY, AND
                      -------------
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF GEORGIA.

          SECTION 12. Entire Understanding.  This Amendment sets forth the
                      --------------------
entire understanding of the parties with respect to the matters set forth
herein, and shall supersede any prior negotiations or agreements, whether
written or oral, with respect thereto.

                                      -4-
<PAGE>

          SECTION 13. Counterparts.  This Amendment may be executed in any
                      ------------
number of counterparts and by the different parties hereto in separate
counterparts and may be delivered by telecopier.  Each counterpart so executed
and delivered shall be  deemed an original and all of which taken together shall
constitute but one and the same instrument.

          IN WITNESS WHEREOF, the parties hereto have caused this Amendment to
be duly executed and delivered in Atlanta, Georgia, by their duly authorized
officers as of the day and year first above written.

                              GLOBAL PAYMENTS INC.


                              By:  ______________________
                                   James G. Kelly
                                   Chief Financial Officer

                                      -5-
<PAGE>

                              BANK ONE, NA,
                              as Administrative Agent, Lender, LC Issuer
                              and Swing Line Lender


                              By: ______________________
                                  Name: ________________
                                  Title: _______________


                      [Signature page to Amendment No. 1]
<PAGE>

                              SUNTRUST BANK,
                              as Documentation Agent and Lender


                              By: ______________________
                                  Name: ________________
                                  Title: _______________



                      [Signature page to Amendment No. 1]
<PAGE>

                              WACHOVIA BANK, N.A.
                              as Syndication Agent and Lender


                              By: ______________________
                                  Name: ________________
                                  Title: _______________


                      [Signature page to Amendment No. 1]
<PAGE>

                              COMERICA BANK,
                              as Lender


                              By: ______________________
                                  Name: ________________
                                  Title: _______________


                      [Signature page to Amendment No. 1]
<PAGE>

             ACKNOWLEDGMENT AND AGREEMENT OF SUBSIDIARY GUARANTORS
             -----------------------------------------------------


          Reference is hereby made to the within and foregoing Amendment No. 1
to Credit Agreement, dated as of March 20, 2001, by and among GLOBAL PAYMENTS
INC., a Georgia corporation ("Borrower"), BANK ONE, NA, a national banking
association, as Administrative Agent, Swing Line Lender and LC Issuer, SUNTRUST
BANK, a Georgia banking corporation, as Documentation Agent, and WACHOVIA BANK,
N.A., a national banking association, as Syndication Agent ("Amendment No. 1";
capitalized terms used herein that are defined in Amendment No. 1 or in the
"Credit Agreement" as defined in Amendment No. 1 being used herein with the
respective meanings assigned to such capitalized terms in Amendment No. 1 or the
Credit Agreement, as the case may be).  Each of the undersigned, which is a
Subsidiary Guarantor under the terms of the Subsidiary Guarantee as provided in
the Credit Agreement, hereby acknowledges and agrees that (i) the undersigned
has consented to the foregoing Amendment No. 1, (ii) the Subsidiary Guarantee
and the other Loan Documents to which each of the undersigned is a party shall
remain in full force and effect on and after the date hereof, and (iii)  each of
the undersigned hereby reaffirms and restates its obligations and liabilities
under the Subsidiary Guarantee and the other Loan Documents to which each of
the undersigned is a party after giving effect to Amendment No. 1.

     This Acknowledgment and Agreement of Subsidiary Guarantors made and
delivered as of March 20, 2001.

                         GUARANTORS:
                         ----------

                         NATIONAL DATA PAYMENT SYSTEMS, INC.,
                         as a Subsidiary Guarantor


                         By: ___________________________
                             James G. Kelly
                             Chief Financial Officer


                         NDC CHECK SERVICES, INC.,
                         as a Subsidiary Guarantor


                         By: ___________________________
                             James G. Kelly
                             Treasurer

                                      -10-
<PAGE>

                         CHECKRITE RECOVERY SERVICES, INC.,
                         as a Subsidiary Guarantor


                         By: ___________________________
                             James G. Kelly
                             Treasurer


                         MERCHANT SERVICES U.S.A., INC.,
                         as a Subsidiary Guarantor


                         By: ___________________________
                             James G. Kelly
                             Treasurer


                         NDPS HOLDINGS, INC.,
                         as a Subsidiary Guarantor


                         By: ___________________________
                             James G. Kelly
                             Treasurer


                         GLOBAL PAYMENT HOLDING COMPANY,
                         as a Subsidiary Guarantor


                         By: ___________________________
                             James G. Kelly
                             Treasurer


                         NDC HOLDINGS (UK) LTD.,
                         as a Subsidiary Guarantor


                         By: ___________________________
                             James G. Kelly
                             Treasurer

                                      -11-
<PAGE>

                         GPS HOLDING LIMITED PARTNERSHIP,
                         as a Subsidiary Guarantor


                         By: GLOBAL PAYMENTS INC.,
                             its general partner


                             By: ___________________________
                                 James G. Kelly
                                 Chief Financial Officer


                         GP FINANCE, INC.,
                         as a Subsidiary Guarantor


                         By: ___________________________
                             Name:
                             Title:

                                      -12-