Labor Seeks Influence in New York's Mayoral Race "Politics in the city are shifting," Michael Mulgrew, president of the teachers' union, the United Federation of Teachers, said. It's not a pipe dream. We're going to be a force. They have so much polling data that they can pinpoint the views of Puerto Ricans and Chinese immigrants alike. They can tailor messages based on brands of toilet paper voters buy. Normally busy handling complaints from teachers, they are now scouring financial records and questioning candidates about $4,000 restaurant bills. And on Wednesday, the union will throw its sophisticated political machine behind a candidate for mayor of New York City. Unions across the city, after years of low morale and stalled contract negotiations, are roaring back to life this election season, excited by the prospect of installing a friend of labor in City Hall when Mayor Michael R. Bloomberg leaves office at the end of the year. Some groups, like the teachers" union, are expected to spend several million dollars on the race. Several labor leaders are weighing advertising blitzes aimed at the broader public. Political organizers are training callers, social media activists and door-to-door canvassers. "Politics in the city are shifting," Michael Mulgrew, president of the teachers" union, said. Labor leaders face several challenges as they seek to reassert themselves as political heavyweights in a city that has not elected a Democrat for mayor since 1989. In a crowded field, they are split over whom to endorse, causing concern that they might cancel one another out. At a time of declining union membership and lingering economic turmoil, the strength of organized labor is unclear. Public officials across the country, including Mr. Bloomberg, a political independent, have cast doubt on their motives, and pushed back against demands from municipal workers for retroactive raises and more generous health benefits. And a new pro-business group in New York is preparing to spend millions on City Council races. Still, political experts say there is potential for organized labor to sway the mayoral election. Analysts expect only modest turnout - around 650,000 voters, or about one-fifth of registered Democrats - in the Democratic primary in September. A runoff election is widely expected, raising the stakes. Each of the city's large unions can be valuable to different candidates. Unions representing lower-paid service workers might be able to deliver black and Latino voters for candidates who will rely more heavily on them, like William C. Thompson Jr., a former comptroller, and Bill de Blasio, the public advocate. The teachers" union, whose membership is more middle-class, says it has a database of 171,000 teachers, retirees and their relatives. "Unions know their membership and can motivate them," said Edward F. Ott, a lecturer at the Joseph S. Murphy Institute for Worker Education and Labor Studies at the City University of New York. The impact may be reduced and spread across a lot of candidates, but they'll definitely have an impact. Exactly how much the unions will spend in the mayoral race depends on several factors, including whether they face competition from other unions or from political action groups seeking to dampen the influence of organized labor. "It could be the wild, wild West," said Neal Kwatra, a Democratic strategist whose clients include unions, "or it could be business as usual." The teachers" union endorsement is considered a prize because of its politically engaged work force, a treasury of at least $2.5 million and a team that has refined its political operations after years of bitter feuds with Mr. Bloomberg. The seven leading Democratic candidates for mayor are mostly in line with the union's ideology, backing its calls to reduce testing and offer more support to failing schools. In recent days, some have stepped up their efforts to court the union's leaders. Mr. Thompson, a former president of the city's Board of Education, recently announced a plan to give each teacher a $200 budget for classroom supplies. On Tuesday, he picked up the support of the principals" union, the Council of School Supervisors and Administrators. Mr. de Blasio, another leading candidate for the teachers" union's endorsement, stood with Mr. Mulgrew last week to denounce high-stakes testing. The union last made an endorsement for mayor in 2001, when it selected Mark Green, a Democrat, over Mr. Bloomberg, then a Republican. It did not enter the contests in 2005 and 2009, wary of Mr. Bloomberg's vast financial resources. Some union officials regretted the decision to skip the 2009 race, after Mr. Thompson, then the Democratic nominee, came within striking distance of Mr. Bloomberg, who spent more than $100 million of his fortune on that race alone.