<PAGE>   1
                                                                  EXHIBIT 10.18



                         [CLARK/BARDES INC. LETTERHEAD]



June 11, 1998

Mr. J. Philip Raiford
Vice President & Product Manager
Brokerage & Corporate Life Insurance
Nationwide Life Insurance Company
One Nationwide Plaza
Columbus, Ohio 43215

RE:  PRODUCTION AGREEMENT

Dear Phil:

Clark/Bardes is entering into a Production Agreement with Nationwide Life
Insurance Company ("Nationwide") in consideration of our continued business
relationship and current financing activities. We agree that Clark/Bardes will
do the following:

1.   Use commercial best efforts to sell and service products offered by
     Nationwide in those markets in which Nationwide is generally recognized as
     being "competitive". For such purpose, "competitive" shall be defined as
     either:

     A. Being one of the top five companies offering products in a particular
        market, or, 

     B. Being in the top 50% of the companies offering products in a particular
        market.

     Such assessment shall be based on all salient product features including,
     but not limited to, cash values, death benefits, compensation, company
     ratings and financial strength, and customer services.

     This effort will be made with both existing clients and future clients
     and/or clients of companies which we acquire.

     This effort will require Clark/Bardes to illustrate and/or present
     Nationwide products in those cases in which Nationwide is "competitive".



<PAGE>   2
Letter to Mr. J. Phillip Raiford
June 11, 1998
Page Two

2.  We agree to commit annually, for a period of 5-years, to produce and sell
    enough business with Nationwide to meet the following criteria:

       o  Clark/Bardes will earn, from Nationwide, a minimum of 10% of its total
          first year annualized commissions in each market that Nationwide
          provides a "competitive" non-exclusive product, or at least 15% of
          such total commissions in all such markets.
                                  
       o  Clark/Bardes will earn, from Nationwide, a minimum of 15% of its total
          first year annualized commissions in each market that Nationwide
          provides a "competitive" exclusive product, or at least 25% of such
          total commissions in all such markets.

       o  Clark/Bardes will earn, from Nationwide, at least $3 million of first
          year annualized commissions during each consecutive 12 month period.

3.  At the end of each 12 month period following the effective date of this
    Agreement, Nationwide will determine if the production criteria in
    paragraph (2) have been met. If Clark/Bardes fails to meet those production
    criteria, Clark/Bardes will have an additional 12 month period to come into
    cumulative compliance determined with respect to paragraph (2).

    The penalty for non-compliance shall be $150,000 for any 12 month period.

4.  Any penalty due pursuant to the formula above shall reduce future
    commissions otherwise due to Clark/Bardes over the subsequent 12 month
    period. If such commission reduction is not allowed under Clark/Bardes'
    current financing documents, other security will be provided.

5.  This letter agreement, which shall be binding upon Clark/Bardes and
    Nationwide, shall be incorporated into a formal document on or before July
    1, 1998, which agreement shall contain provisions regarding, among others,
    term and termination, confidentiality, governing laws, and legal opinions
    from Clark/Bardes outside counsel regarding this agreement.

Signed



/s/ MELVIN G. TODD                          /s/ J. PHILIP RAIFORD
----------------------------                ----------------------------
Mr. Melvin G. Todd                          Mr. J. Philip Raiford
President                                   Vice President & Product Manager
Clark/Bardes, Inc.                          Brokerage & Corporate Life Insurance
                                            Nationwide Life Insurance Company


6/12/98                                     6/12/98
-------                                     -------
Date                                        Date

CLARK/BARDES
          inc.



<PAGE>   3

                        [CLARK/BARDES, INC. LETTERHEAD]

                                                                   June 11, 1998




VIA FACSIMILE

Nationwide Life Insurance Company
Attention: Mark Poeppelman
One Nationwide Plaza (1-32-05)
Columbus, Ohio 43215-2220


Ladies and Gentlemen:

          In anticipation of the initial public offering (the "IPO") of common
stock in Clark/Bardes Holdings, Inc. ("CBH"), Clark/Bardes, Inc., a Texas
corporation ("we" or "the Company"), has offered to purchase from you the
Common Stock Purchase Warrants (the "Warrants") of the Company issued to and
held by you pursuant to that certain Note and Warrant Purchase Agreement dated
as of September 8, 1997 (the "Agreement").

          On the terms and conditions herein stated, we agree to purchase the
Warrants, and by your execution hereof you agree to sell the Warrants, for the
consideration set forth on Annex A hereto. Upon the purchase and sale of the
Warrants as contemplated hereby, the Registration Rights Agreement and the
Participation Rights Agreement (as both such terms are defined in the
Agreement) shall be of no further force and effect, and the Company shall
immediately cancel the Warrants.

          Our obligation to purchase the Warrants, and your obligation to sell
the Warrants, are expressly conditioned upon the satisfaction of each of the
following conditions precedent:

<PAGE>   4

                                      -2-                   June 11, 1998


         (a)       The IPO shall have been consummated not later than December
31, 1998;

         (b)       CBH shall have received net proceeds from the IPO (i.e., net
of underwriting discounts and commissions and net of expenses payable in
connection with the IPO) of at least $35,000,000; and

         (c)       CBH shall have contributed at least 95% of the net proceeds
from the IPO to the Company (or to its successor from the contemplated
reincorporation merger of the Company with and into Clark/Bardes, Inc., a
Delaware corporation).

         In order to induce you to enter into this letter agreement, the Company
hereby represents and warrants as of the date hereof and, except with respect to
the representation and warranty set forth in clause (v) below, as of the date of
the sale and purchase of the Warrants, as follows:

         (i)       The Company has all requisite corporate and other power and
authority to execute, deliver and perform its obligations under this letter
agreement.

         (ii)      The execution, delivery and performance by the Company of
this letter agreement have been duly authorized by all requisite corporate
action on the part of the Company. The Company has duly executed and delivered
this letter agreement, and this letter agreement constitutes the legal, valid
and binding obligation of the Company, enforceable against the Company in
accordance with its terms.

         (iii)     Neither the execution and delivery of this letter agreement
by the Company nor compliance by the Company with the terms and provisions
hereof, will conflict with, or result in a breach of the terms, conditions or
provisions of, or constitute a default under, or result in any violation of, or
result in the creation of any security interest, lien or other encumbrance upon
any of the properties or assets of the Company pursuant to, its articles of
incorporation or bylaws, any award of any arbitrator or any agreement (including
any agreement with shareholders), instrument, order, judgment, decree, statute,
rule or regulation to which the Company is subject.

         (iv)      No authorization, consent, approval, exemption or other
action by or notice to or filing with any court or administrative or
governmental body or any other person or entity is required in connection with
the execution and delivery of this letter agreement by the Company or the
fulfillment of or compliance with the terms and provisions hereof by the
Company.

         (v)       The current Exercise Price (as defined in the Warrants) of
the Warrants is $2.95 per share, and no event has occurred since September 8,
1997 which, under the terms of the Warrants, would cause or require an
adjustment to such Exercise Price.
<PAGE>   5

                                      -3-                   June 11, 1998


required in connection with the execution and delivery of this letter agreement
by the Company or the fulfillment of or compliance with the terms and provisions
hereof by the Company.

         (v)  The current Exercise Price (as defined in the Warrants) of the
Warrants is $2.95 per share, and no event has occurred since September 8, 1997
which, under the terms of the Warrants, would cause or require an adjustment to
such Exercise Price.

If you are in agreement with the foregoing, please sign in the space provided
below and fax a copy of this letter agreement to the Company (214) 871-7690,
Attention: Melvin G. Todd, whereupon this letter agreement shall become a
binding agreement between us.


                                                  Very truly yours,

                                                  Clark/Bardes, Inc.


                                                  By: /s/ MEL TODD
                                                     --------------------------
                                                     Name:  Mel Todd
                                                           --------------------
                                                     Title: President & CEO
                                                           --------------------
       


Nationwide Life Insurance Company

By:  /s/ MARK W. POEPPLEMAN
   ----------------------------------
   Name: Mark W. Poeppleman
         ----------------------------
   Title:Investment Officer
         ----------------------------
<PAGE>   6
                                     -4-


                                   Annex A

                    CONSIDERATION FOR PURCHASE OF WARRANTS

Consideration for Nationwide Life Insurance Company's sale to the Company of
1,016,949 Warrants issued pursuant to that certain Note and Warrant Purchase
Agreement dated as of September 8, 1997 is as follows:

     1)  The greater of (a) 75% of the IPO price, less $2.95 per share
         multiplied by 1,016,949, provided that if, at any time after the date
         hereof and prior to the purchase and sale of the Warrants, any stock
         split, reverse stock split, reclassification or other event occurs
         which would cause the Exercise Price (as defined in the Warrants) of
         the Warrants to be adjusted or cause the number of shares of the
         Company to be adjusted according to the terms of the Warrants
         (including, without limitation, the merger of the Company with and
         into Clark/Bardes, Inc., a Delaware corporation, as contemplated in
         the draft registration statement for the IPO previously provided to
         you), then in each such case the above-specified price per share of
         common stock or number of shares of common stock shall be
         proportionately adjusted; or (b) $1,600,000; and

     2)  Simultaneously with the execution of this letter agreement, the
         execution by the Company of that certain letter of agreement between
         the Company and Nationwide Life Insurance Company dated June 11, 1998.


Within 15 days of the IPO being consummated, any amounts due to Nationwide will
be paid by wire transfer of immediately available funds for credit to an
account designated by Nationwide at a later date.

Nationwide Life Insurance Company


By:  /s/ MARK W. POEPPELMAN
    -----------------------------

     Mark W. Poeppelman
---------------------------------
[Printed Name]

     Investment Officer
---------------------------------
[Title]


CLARK/BARDES, INC.


By:  /s/ MEL TODD       
    -----------------------------

     Mel Todd                 
---------------------------------
[Printed Name]

     President & CEO   
---------------------------------
[Title]