In this season of jockeying for endorsements, there are plenty of mayoral candidates who want to show they feel labor's pain under Mayor Michael Bloomberg.  And yet, whoever wins will have a multi-billion dollar backlog of expired labor contracts.  Before any of them gets to negotiate with the unions, though, they first have to get through the election.

Labor's resurgent resentment toward Mayor Michael Bloomberg was evident at back-to-back protests on city hall steps this week.

The protest wasn't specifically about the teacher evaluation deal that collapsed last week, costing the city hundreds of millions of dollars in state and federal funds.  But it was the clear backdrop.

The striking school bus drivers were there. So was teacher’s union president Michael Mulgrew who was calling for a moratorium on closing underperforming schools. And three top Democrats running for mayor.

“The reason you’ve got a huge crowd of people on the city hall steps in the freezing cold is because enough is enough,” Public Advocate Bill de Blasio told the crowd.  "There have been so many attempts to get this administration to be reasonable, to work with parents, to work with teachers, to work with principals, and it's fallen on deaf ears."

Current comptroller John Liu declared it was time to “stop playing shell games.” Former comptroller Bill Thompson added, “school closings aren’t a policy.”

The protests drew cheers from the crowd of parents and union backer, and a chorus of complaints from charter school supporters. Howard Wolfson, a deputy mayor under Bloomberg, tweeted that the scene was quote “a scary look at New York City’s possible future."

Missing from the picture was Council Speaker Christine Quinn, the Democrat leading polls.

While the rally was going on outside city hall, she was talking to reporters inside. 

“I don’t typically go to press conferences where I don’t support the positions that are being called for,” Quinn said when she was asked about skipping the union event.

Quinn is trying to carve out centrist positions on the city’s most divisive union issues. She generally supports the substance of many Bloomberg policies, but wants them carried out in a less combative, more inclusive way.

“So I wasn’t outside because although I support a very significant change in the number of schools we close and how we close schools, I do not support a moratorium,” she said.

There's a subtext to Mayor Bloomberg’s latest confrontations with city workers. After eight years of Giuliani and twelve of Bloomberg, who will unions be negotiating with next?

Because, as Michael Mulgrew told the crowd of protesters, he's just waiting out the next eleven months of Bloomberg's term.

“We’ve given up trying to work with this administration. We’ve given up,” Mulgrew said.

That includes negotiating a new contract. Theirs expired three and a half years ago, and they aren't the only ones. Police, firefighters and other civil service workers are also working on expired contracts. 

“It’s the worst that I’ve ever seen,” said Councilman Robert Jackson, the chair of the Education Committee who previously worked for a public employees union. “And in fact, whoever the new mayor is, is going to have the unions not knocking on the door, banging on the door, for relief as far as raises, as far as benefits, what have you. And the impact is clearly going t o be felt.”

That's an anxiety Republicans are hope to work to their advantage. Candidate George McDonald raised the specter of unions and special interests taking over the city when he announced his run earlier this month. Former MTA Chairman Joe Lhota is playing up his record as a businessman, but one who worked with unions under Giuliani and in the private sector at Madison Square Garden.

But the ideological leanings of a new mayor will only go so far, says Richard Steier, editor of the civil service union newspaper The Chief, particularly with the major budget challenge of all those expired contracts.

“Because eventually they’re going to reach agreements and there’s going to be a boatload worth of retro-active pay that is going to have to be given to employees,” Steier said.

That backpay boatload, the city’s Independent Budget Office says, could exceed $5 billion.