Limit the state's ability to bank statewide mills

SB 351 limits Montana local governments' ability to save ("bank") property tax authority for certain state-mandated tax programs. It specifically amends property tax law to prevent local entities from carrying forward unused mill authority (tax rate allowances) for taxes imposed under statutes 20-9-331, 20-9-333, 20-9-360, and 20-25-439. This change directly affects counties, cities, and school districts that rely on these specific state tax programs, requiring them to use their full annual tax authority each year rather than saving it for future use. The bill’s key provision removes these programs from the existing rule that allows governments to carry forward unused tax authority to future years.