Boston Mayor Thomas Menino on Monday said he would decide “very shortly” on whether to endorse U.S. Sen. Scott Brown or Democrat Elizabeth Warren in this year’s Senate contest as labor leaders and politicians cast the November election as a fight between the “haves” and the “have-nots.”

The Greater Boston Labor Council held its annual Labor Day breakfast at the Park Plaza hotel on Monday morning, drawing a crowd of union officials, Democratic politicians and elective-hopefuls as labor defended against a perception that its influence in politics is on the wane.

The event featured a heavy dose of anti-Mitt Romney and Scott Brown rhetoric, and local labor leaders were urged to talk to their members and get out the vote in Thursday’s primary and the November general election.

Upon arriving shortly after the start of the breakfast and taking her seat next to Menino, Warren received a hearty welcome and a standing ovation from the audience. During her remarks, she praised Menino’s leadership and even kissed him goodbye on the cheek when she left.

“Unions helped build America’s middle class, and it’s unions who are going to fight to keep America’s middle class,” Warren said.

“Washington is rigged to work for the big guys. It’s rigged to work for the guy who can hire an army of lobbyists and lawyers. We want a Washington for the working people,” Warren said.

Despite Menino saying that Brown has had an inconsistent record of voting for Massachusetts working families, the powerful Boston mayor has yet to endorse Warren and his words were being closely monitored on Monday by those in attendance due to the strong political organization he commands in the city.

“We’ll make a decision very shortly and we’ll have an impact on the election whoever we support,” said Menino, who called it still early yet with 64 days until the election.

Menino also had harsh words for Republican presidential nominee Mitt Romney and his running mate U.S. Rep. Paul Ryan, who he said have expressed a vision of limited government that would break the safety net that he said has longer offered a “hand up” to those in need.

“What I heard in Tampa was we’re going to cut these programs. Medicare is going to be a voucher system now? Gimme’ a break. When Mitt Romney signed health care in Massachusetts I was there. The greatest TV production ever. He was so happy about it. Now it’s bad. It’s like a windmill. One day you’re with us, one day you’re against us,” Menino said.

Asked about seeking Menino’s endorsement, Warren said, “I’m out there every single day working for every single vote.”

Candidates in close races this September and November were given seats at the head table and a chance to address the labor crowd, including Warren, U.S. Rep. John Tierney, Joseph Kennedy III and U.S. Rep. William Keating, who delivered a rousing, animated plea to reject the Republican agenda being pushed in Washington.

Brown was also knocked by speakers for his votes to repeal prevailing wage laws for public projects and against bills that would have provided stimulus funds for construction, supported college scholarships and extended unemployment benefits for Massachusetts workers.

“When it came time to choose, Elizabeth Warren traded in her consumer advocate costume, and took a quarter million dollar payday to fight on behalf of a corporate insurance giant against laborers suffering from asbestos poisoning. Rather than distorting and misrepresenting Scott Brown’s pro-jobs, pro-worker record, she should be explaining the many contradictions in her own record,” Brown spokeswoman Alleigh Marre said in a statement to the News Service.

The Massachusetts Republican Party also called on Warren to apologize for accepting over $200,000 from Travelers Insurance defending the nation’s largest insurer against future lawsuits from asbestos victims.

“While Warren laughed all the way to the bank, these sickened middle-class workers are left with measly lifetime payouts that total 1/40th of Warren’s big payday. Professor Warren owes these laborers an apology for putting her own financial gain ahead of their safety and well-being,” said Nate Little, executive director of the MassGOP.

Warren’s campaign did not immediately respond to a request for comment.

The Labor Day breakfast came at a time when organized labor is viewed by some as fractured and a shell of the influential political force it once was in Massachusetts. Brown capitalized on a significant union support in 2010 when he upset Attorney General Martha Coakley in the special election to fill the late Edward Kennedy’s seat.

“That looked like a pretty energized group to me,” Warren said, dismissing concerns that labor would not be there to help her in November.

Rich Rogers, of the Greater Boston Labor Council, kicked off the morning with a plea to get involved in the 2nd Essex Senate District, where the union-endorsed John Slattery, a former state representative, is running against three other Democrats.

“The other Democrats have been going around saying labor isn’t there. They can’t deliver...,” Rogers said. “If labor goes out there and does their job on the North Shore, we will win and we will send a message. If we can’t win, then we have a serious problem.”

Massachusetts AFL-CIO Massachusetts President Steven Tolman said a decline in donations to political candidates from unions could be due to the emphasis being put on giving local leaders the information and tools they need to drive turnout from the “bottom up.”

Tolman said Brown’s voting record on labor issues “stinks” and believes union members will be there to vote in November if they know his record.

“On all these commercials you hear on the radio every 10 minutes [he] says a lot of nice things that are special about Massachusetts but he neglects the most important thing: His voting record. And his voting record is clearly one-sided toward the haves and it seems like he’s totally forgotten the middle class and the have-nots so we think it’s important that our members are informed properly to make an intelligent decision and not be swayed by fancy commercials,” Tolman said.

Menino called Boston a “union city,” and said he believes labor groups are working hard for Warren and membership in some unions is on the rise.

“It’s all about who the candidate is too. You can’t sell a bad candidate no matter who you are or what organization you are…,” Menino said. “People are smarter than they were in the past. They don’t follow the crowd. They look at the candidate and see what they stand for and that’s what this election is all about.”

Mark Bernard, a staff representative with AFSCME Council 93 in Boston, said a Menino endorsement would help Warren, but he said he believes she can win without it and labor groups will be there to support her.

“I don’t think we’ve lost our juice,” Bernard said.