A state Senate measure dramatically overhauling the pension plans for many future public employees has been introduced, setting off a highly anticipated election-year fight between unions and Republican legislative leaders.

The bill (SPB 7046), which was filed Monday, would close the Florida Retirement System to most new public employees, instead shifting them to either the state’s existing 401(k)-style investment plan or a new “cash balance plan.” Law-enforcement officials and firefighters would still be allowed to join the traditional pension plan.