(1) Except as provided in subsection (2) of this section, each employer shall retain from the earnings of each worker that amount as shall be fixed from time to time by the director, the basis for measuring said amount to be determined by the director. The money so retained shall be matched in an equal amount by each employer, and all such moneys shall be remitted to the department in such manner and at such intervals as the department directs and shall be placed in the supplemental pension fund: PROVIDED, That the state apprenticeship council shall pay the entire amount into the supplemental pension fund for registered apprentices or trainees during their participation in supplemental and related instruction classes. The moneys so collected shall be used exclusively for the additional payments from the supplemental pension fund prescribed in this title and for the amount of any increase payable under the provisions of RCW
51.32.075, as now or hereafter amended, and shall be no more than necessary to make such payments on a current basis. The department may require a self-insurer to make any additional payments which are payable from the supplemental pension fund and thereafter such self-insurer shall be reimbursed therefrom.