Members of New York City’s powerful labor unions are usually hard at work in the days leading up to elections, working phone banks, putting up posters, and handing out leaflets to get out the vote for their union’s candidate. On election days, they typically turn out in large numbers to knock on doors, drive voters to the polls, and volunteer at polling places.

This year, however, many of the major unions, which usually support Democratic candidates, either haven’t endorsed a mayoral candidate or have come out behind Mayor Bloomberg, and the environment is different.

“The foot soldiers of primary day are mostly union members,” a longtime political consultant, Norman Adler, said. “So if the unions are not endorsing a candidate in this primary, there will be less people out there handing you a palm card at the voting booth or at the subway stop. …There will be fewer phone calls.”

The Democrats said they are not concerned about the relative lack of union participation in this year’s primary.

“Our campaign has never been predicated on big endorsements or political machines or anything like that,” Rep. Anthony Weiner’s campaign spokesman, Anson Kaye, said. “We’ve had the same strategy all the way through. That is, drive a campaign based on ideas that animate voters.”

He said the campaign is “thrilled” by the union support it has received – the Uniformed Firefighters Association backed the Brooklyn-Queens congressman yesterday – and believes Mr. Weiner’s campaign themes appeal to working New Yorkers.

A spokesman for the campaign of City Council Speaker Gifford Miller, Reggie Johnson, said union members, who are largely Democratic, would turn out in the primary, union endorsement or not.

“Democrats will vote for the candidate who has a clear record of fighting to protect traditional progressive values, from leading the fight to enact the city’s first earned income tax credit to securing vital education funding,” Mr. Johnson said. “Gifford Miller is that candidate.”

Union leaders and political observers, however, said the absence of union workers from the election process this week will represent a major blow to the Democrats and could help the Republican incumbent.

“Ours is not a paper endorsement. It’s an endorsement in which they’re guaranteed that there’s going to be workers and people working on their behalf, 110 percent,” the political director of District Council 37, Wanda Williams, said. The union has endorsed Mr. Bloomberg for re-election.

Ms. Williams said DC-37’s executive director, Lillian Roberts, would be marching with Mr. Bloomberg in Saturday’s Labor Day parade. Already the union has sent mailings to members, notifying them that, while Mr. Bloomberg doesn’t face a primary challenge, when Election Day arrives in November, “We’d be expecting that they vote for him and urging them to do so.”

On primary day alone, Ms. Williams said, the Democrats are missing out on more than 1,000 DC-37 volunteers. On Election Day, that number could jump to more than 2,500.

The political director of the health care workers union, Local 1199, Jennifer Cunningham, said the health care workers’ endorsement helps increase voter turnout. It also gives candidates extra visibility, as well as volunteers to help with poll watching, door knocking, and phone-bank work.

In 2001, the powerful union endorsed Fernando Ferrer the day after Labor Day, but this year, she said, “it is getting less likely” that the 1199’s leaders will vote on a pre-primary endorsement. She said the union would reconsider an endorsement after the primary.

“I think there are a variety of opinions in the union about which direction to go,” she said. “We just have not come to a decision.”

In the meantime, the Democrats, and Mr. Ferrer in particular, are left without the union’s help.

“It’s a huge loss to the Ferrer campaign because it’s a very well-oiled political machine at 1199, and they’re capable of providing enormous resources, fast,” Mr. Adler said.

The president of the United Federation of Teachers, Randi Weingarten, also said the absence of the unions could have an impact on primary day.

“It does certainly change elections when the UFT is not involved, and you’ve had two big unions that are not involved, 1199 and the UFT,” she said. “Given that it’s a very competitive election, it may have been a significant factor. I expect that if we were involved, it would have had a great impact, but that’s looking at a crystal ball.”