(1)    The sum of all employee post-tax contributions allocated to a participant’s account may not in any calendar year exceed the maximum contribution limitation established under section 415 (c) of the Internal Revenue Code, as adjusted under section 415 (d) of the Internal Revenue Code and any applicable regulations adopted by the federal department of the treasury.

   (2)   The department may provide by rule additional limitations for participants who are participating in more than one retirement system.

   (3)   Any contribution that the department receives, which is allocated to the account of a participant and which exceeds the contributions limitation under this section, may be refunded or credited as provided in s. 40.08 (6). If the department refunds any contributions that exceed the limitation under this section, the department shall first refund amounts voluntarily contributed by a participating employee as an additional contribution under s. 40.05 (1) (a) 5.