(a) If the employees of the fire department of a municipality, with the consent of the municipality, elect to become members of the retirement system, the funds of the municipality's firemen's relief and retirement fund, if any, and future payments to the fund may be transferred to the board of trustees on the voluntary application of the municipality.
(b) A participating municipality shall pay to the board of trustees money that could have been paid annually to the firemen's relief and retirement fund if the fire department were not covered by the retirement system or another pension system or if the municipality had taken the proper steps to secure the money. The retirement system shall credit amounts paid under this subsection for the benefit of fire fighters as the board of trustees directs.