The Appleton-area bus system could shut down by the end of May if the Legislature approves a budget-repair bill that slices public employees' collective bargaining rights, Appleton Mayor Tim Hanna warned Wednesday.

Reducing bargaining rights for transit workers would lead the federal government to cut off $46.6 million in aid to Wisconsin bus systems, including $2.5 million to Valley Transit, according to the nonpartisan Legislative Fiscal Bureau and the Wisconsin Urban and Rural Transit Association.

The impact on bus systems would vary, depending on their structure and the timing of their labor contracts and federal grants.

The Assembly on Wednesday tabled an amendment to exempt transit workers from the union changes.

Gov. Scott Walker's budget-repair legislation would boost pension and health care contributions for most state and local government and school district employees and prohibit their unions from bargaining on anything except wages. Police officers, firefighters, deputy sheriffs and state troopers would be exempt from those changes.

Federal law, however, requires transit workers' bargaining rights to remain intact to receive federal transit aid. The bill would not affect bargaining rights or federal aid at the Milwaukee County Transit System and most suburban bus systems because they are operated by private companies.

But the bill would affect other bus systems run by public employees, the fiscal bureau and the transit association say. Valley Transit - which carries about 1 million riders a year to work, school and elsewhere - could be the first to fall because of its complex funding structure, Hanna said.

Valley Transit funds its $7.8 million annual budget from six municipalities, four towns, three counties, the state and federal governments and passenger fares, but "the funding is so intertwined that when you pull out a major piece of it, the whole thing starts to fall apart," Hanna said.

Cullen Werwie, Walker's spokesman, reiterated his earlier statement that bus systems could keep their federal funding if the bill is approved. He did not elaborate.

The amendment tabled Wednesday, on a 58-38 party-line vote, would have grouped transit workers with public safety workers to keep their bargaining rights. Democrats voted in the minority.

The fiscal bureau and U.S. Labor Department have suggested transit systems could preserve their federal aid by turning their operations over to private transit companies.

Madison Metro Transit dropped that structure years ago and converted its transit workers into city employees so they would be prohibited from striking, Madison City Attorney Michael May said.

The process of privatizing could take two or three years, transit association lobbyist Gary Goyke said.

The federal provision protecting union rights was part of the 1964 Urban Mass Transit Act. Union backers defeated an earlier version of the legislation, without the bargaining protections, because of fears that transit workers would lose bargaining rights if local governments took over private bus companies in states that banned public-sector employee unions.