ity Councilor Francis ''Mickey'' Roache sponsored the living wage ordinance that boosted workers' wages in Boston and was the only at-large council candidate endorsed by labor last fall.
Two weeks ago, he demonstrated with city employees who are members of the American Federation of State, County, and Municipal Employees, as they toted a giant toothbrush and demanded dental benefits. Then Roache declared a prolabor position on the council's highest-profile issue, saying the city should give its workers raises before it helps the Red Sox build a new ballpark.
But siding with labor is not so simple in the intricate, high-pressure politics that confront the City Council this year.
While Roache's position has pleased city employees' unions, some usually friendly building trades unions, whose members are eager for construction jobs, are warning Roache that his opposition to the Fenway project could cost him their support.
The Sheet Metal Workers have already threatened to abandon him. About 40 carpenters and electricians flooded last week's council meeting to put a face on their position that the building trade unions want the construction work from a new Fenway Park and related infrastructure improvements.
They want this project so fiercely that Joe Nigro, leader of the Building & Construction Trades Council, has made it plain that councilors who oppose it will pay.
''In labor, you have to be 100 percent,'' said Roache. ''It comes down to perception.''
The upcoming City Council vote on the new baseball park is not just a test of the council's will to stand up to Mayor Thomas M. Menino, who is pushing the Fenway plan. It is also a chance for the city's construction unions to demonstrate their might.
The vote may be months away, but Roache and other councilors are already feeling the tugs of various unions. But Roache and other councilors have already done the political calculations and decided that city employees come first.
Some councilors immediately staked their ground on the Fenway proposal by saying they would not consider the deal until the administration settled unresolved public employee contracts, which administration sources say will happen soon.
''It would be very difficult for us to sit there and vote to give millions of dollars to a private organization and not fulfill the obligations of these city contracts,'' said Councilor Brian Honan (Allston-Brighton).
By measure of influence, the trade unions rank third to city employees and senior citizens as a vote to covet. Unions not only help candidates fund campaigns, but offer phone banks at union halls and members to stand out and work the voters. Some councilors define themselves by their pro-union stances; Council President James M. Kelly is recording secretary of the sheet metal workers union.
Menino's administration sees Roache and Kelly as two councilors particularly vulnerable to pressure from building trades unions.
Administration sources say that so far they haven't asked the unions to mount pressure on councilors but are banking on that pressure to swing at least those two votes.
The administration needs to win over three of seven opponents to gain approval of the Red Sox plan, which relies on $212 million in city funding for a parking garage and land acquisition costs, which would be repaid by user fees.
But Kelly has spoken out adamantly against the plan, and Roache said he is not going to switch, even if it means losing support from the unions.
''If the administration thinks that's what's going to make the difference, they shouldn't waste any time on me,'' Roache said. ''I'm going to continue on. If that means my political demise, so be it.''
Roache and Councilor Peggy Davis-Mullen, who are both considering running for mayor next year, have also said that their constituents are against public financing for a ballpark. Davis-Mullen, who got a vital boost from labor with Kelly's help in her 1997 campaign, said she is opposed to spending public money on private land for a private corporation, a strong personal position she likened to a stance on abortion. The question is more nuanced, she said, than a simple pro- or antilabor vote.
''There comes a time you have to say, philosophically, I don't believe in taking land for a private purpose,'' Davis-Mullen said. ''I'm not saying I don't want the work, but there are other ways to finance it.''
Nigro doesn't buy that argument, saying that the city will benefit from the state's commitment of $100 million for infrastructure improvements in the Fenway and from an expanded tax base.
''If there is opposition just for the sake of opposition and without clear thinking and clear negotiating, not tying every little problem that every city councilor has into this deal, then it could create a labor vote'' against councilors who oppose the park, he said. ''We have an awful lot of good friends on the City Council; we always have; and we see this just as a red herring by the City Council.''
Conversely, Roache said the council cannot turn back.
''If we buckle on this, I don't think the council will recover,'' Roache said. ''We have to stand strong. A lot of lines have been drawn in the sand.''
Steven Wilmsen of the Globe Staff contributed to this report.