Philadelphia Mayor Michael Nutter's legal crusade to force pension and benefit changes on unionized city workers has been joined by thousands of interested parties on both sides.

AFSCME District Council 33, Philadelphia's largest municipal union, has worked without a new contract for more than three years, and Nutter wants members to accept money-saving pension and health benefit changes.

But as I wrote here last month, a 1993 case makes Pennsylvania law unique in preventing a public employer from imposing new terms in a case where the parties can't agree and workers keep working under the terms of the old agreement.

The city's chief labor negotiator, Shannon Farmer, says that means unions can prevent any government facing a financial crisis from adjusting labor costs, even if its contractual obligation to workers has expired.

"In effect the unions -- not the employers, not the taxpayers -- are getting to decide how the budget should be balanced, because they're sitting there and saying, 'You can't do anything to touch this item of the budget,'" Farmer said in a telephone interview. "Health-care costs go up by a million dollars? The union can basically just say, 'Eat it, that's not our problem.'"

And so, associations representing more than 3,000 Pennsylvania cities, counties, townships and school districts have filed a brief supporting Nutter's position in the case. On the other side, the Philadelphia union has been joined by the state's largest labor organizations, representing more than a million employees.

Their attorney, Bruce Ludwig, said public employees' right to strike in Pennsylvania is limited, and to balance that, the law limits employers' ability to impose new terms on workers. He says a ruling in Nutter's favor would be unjust.

"This would, if accepted, change that balance so that an employer would just go, 'Well, we want to reduce your benefits, we want to reduce your wages or increase your health-care cost, and we're just going to go ahead and do that,'" Ludwig said.

Nutter wants the state Supreme Court to take the case directly and revisit the law on imposing new terms. Unions say the dispute should work its way up the legal system. That course could take so long that Nutter's second term would expire before the case is resolved.

You can read the unions' legal brief here, and the employers' brief here.