An increased employer payment contribution that results in a lower taxable wage shall not be considered a violation of the applicable prevailing wage determination so long as all of the following conditions are met:

1. (a) The increased employer payment is made pursuant to criteria set forth in a collective bargaining agreement.
2. (b) The increased employer payment and hourly straight time and overtime wage combined are no less than the general prevailing rate of per diem wages.
3. (c) The employer payment contribution is irrevocable unless made in error.