(1) An employees retirement system is hereby established for the purpose of providing a retirement annuity or other benefits for employees as provided by the State Employees Retirement Act and sections 84-1332 and 84-1333. The retirement system so created shall begin operation January 1, 1964. It shall be known as the State Employees Retirement System of the State of Nebraska and by such name shall transact all business and hold all cash and other property as provided in such sections.
(2) The retirement system shall not accept as contributions any money from members or the state except the following:
(a) Mandatory contributions established by sections 84-1308 and 84-1309;
(b) Money that is a repayment of refunded contributions made pursuant to section 84-1322;
(c) Contributions for military service credit made pursuant to section 84-1325;
(d) Actuarially required contributions pursuant to subdivision (4)(b) of section 84-1319;
(e) Trustee-to-trustee transfers pursuant to section 84-1313.01; or
(f) Corrections ordered by the board pursuant to section 84-1305.02.