Where a collective bargaining agreement is entered into with an employee representative organization, the school board may include in the agreement a provision requiring employees covered by the agreement who are not members of the representative organization to pay their proportionate share of the cost of the collective bargaining process and contract administration, measured by the amount of dues uniformly required by members. In such case, proportionate share payments shall be deducted by the board from the earnings of the non-member employees and paid to the representative organization.