Giving Senator Barack Obama new momentum, one of the nation’s largest labor unions, the United Food and Commercial Workers, endorsed him on Thursday. Another giant, the Service Employees International Union, was on the brink of backing him.
The endorsement of the service employees, which with 1.9 million members is seen as the nation’s most politically potent union, would be considered a special boon. Members of the service employees’ board were casting votes by e-mail and fax on Thursday night, and two top S.E.I.U. leaders said an Obama endorsement was likely.
The two unions did not make endorsements until now largely because they were so torn among Mr. Obama, John Edwards and Senator Hillary Rodham Clinton. But with Mr. Edwards out and Mr. Obama winning eight straight contests, many of the top leaders of the unions decided it was time to back him.
“Both candidates are good on worker issues, but there is something about Senator Obama that has mobilized our leadership and mobilized our membership,” said Joseph Hansen, president of the food and commercial workers, which represents 1.1 million workers in the United States. “Forty percent of our members are less than 30 years old, and a lot of them like Obama.”
The two endorsements could go far to help Mr. Obama, of Illinois, increase his support among Hispanics, who have overwhelmingly favored Mrs. Clinton, of New York. The two unions have many immigrant members.
The service employees represent janitors, nurses, nursing home workers and home-health workers, while the food and commercial workers represent supermarket, warehouse and meat-processing workers.
The S.E.I.U. has especially strong ties with the nation’s Hispanic leaders because it played a major role in the campaign to win a path to legalization for the nation’s illegal immigrants.
One top service employees’ official said the union was moving to endorse Mr. Obama now because many leaders hoped the nomination could be decided without a fractious fight at the Democratic convention in August. “It’s a two-person race and we want to be involved,” said the official, who insisted on anonymity because the union is not scheduled to formally announce its endorsement until Friday. “It’s not an anti-Hillary move.”
Unlike the service employees, the United Food and Commercial Workers is not known for its political muscle, but it has many members in several states with contests coming up: Ohio, Pennsylvania, Texas and Wisconsin.
“Obama is the front-runner now, and we decided now was the time to make an endorsement,” Mr. Hansen said.
When the service employees’ national board failed to agree on an endorsement last October, it gave its state chapters permission to make endorsements. The S.E.I.U.’s California state chapter endorsed Mr. Obama several days before the primary there on Feb. 5, but Mrs. Clinton handily won the state. Service employee officials said they did not have enough time to muster a full-throated campaign on Mr. Obama’s behalf, asserting that if they had several weeks they could have helped persuade many Hispanic voters to back him.
Mrs. Clinton has the endorsements of two other large, politically savvy public-sector unions that have campaigned for her: the American Federation of State, County and Municipal Employees and the American Federation of Teachers.