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(WASHINGTON) — Despite a cascade of defections from within his own party in recent weeks, President Joe Biden has been able to count on labor unions as a bulwark against diminishing support for his re-election bid. That backing has begun to weaken, however, placing further pressure on Biden at a moment of peril for his campaign.

A 55,000-member union local in the Pacific Northwest on Friday issued a public letter calling on Biden to end his candidacy. Democratic members of Congress with close ties to labor on Friday also joined the roster of elected officials calling on Biden to step aside.

Local 3000 of the United Food and Commercial Workers, the union in the Pacific Northwest, released a letter on Friday that said Biden should leave the race. The labor organization did not endorse Biden in this year’s Democratic primary, opting to weigh in as “uncommitted,” but it has vowed to support whoever the party nominates for the general election.

“We call on President Biden to pass the torch to the next generation. He has much to celebrate over his career of accomplishments fighting alongside working people, but it is time for him to retire with dignity, and campaign as hard as we all will for an alternative candidate,” the union’s letter said. “The stakes are simply too high to do otherwise.”

Sen. Sherrod Brown, D-Ohio, among the top allies of organized labor in the chamber, called on Biden to end his re-election bid on Friday. Democratic Rep. Mark Pocan, of Wisconsin, co-founder and co-chair of the House Labor Caucus, did the same.

Two allies of Biden in the labor movement told ABC News that he should step aside and a third said it would support an alternative Democratic nominee. The labor allies requested that ABC News not publish their names due to the sensitivity of the issues surrounding Biden’s candidacy.

A union with a presence in several battleground states, which endorsed Biden, told ABC News that it would back an alternative candidate at the top of the Democratic ticket.

A labor leader, who also endorsed Biden, told ABC News that they believe Biden should leave the race, praising Biden for his pro-labor policies but warning of the threat to workers presented by his Republican opponent, former President Donald Trump. “I think the time has come,” they said.

Concern about Biden is widespread among union officials, the labor leader said. “There’s not a person in the labor movement who isn’t worried,” they added, pointing to Biden’s unsteady debate performance and weakened election prospects. “Unions are looking at the same thing that everybody else is looking at.”

Another labor leader, who has publicly supported Biden, said it is time for him to step aside from his campaign. The person similarly cited the risk posed by Trump, including the potential to undo Biden’s achievements in office. “Let’s secure his legacy and build on it,” they said. Worry about Biden is pervasive among union officials, but they risk fracturing the support of voters if they speak out publicly, the person added.

Sean O’Brien, president of the 1.3-million member International Brotherhood of Teamsters, which endorsed Biden in 2020, spoke at the Republican National Convention this week. “We are not beholden to anyone or any party,” O’Brien told the audience in Milwaukee, Wisconsin. “We want to know one thing: What are you doing to help American workers?”

The speech angered White House officials, Congressional Democrats and other labor leaders, the Washington Post reported.

The Teamsters did not immediately respond to ABC News’ request for comment. In a statement to the Post, Teamsters spokesperson Kara Deniz said: “The Teamsters refuse to be pressured to fall in line by those who continue to applaud a broken system,” Deniz continued. “We will continue to participate in the political process at all levels on behalf of working people.

In a statement to ABC News, the Biden campaign touted the president’s record on labor issues, contrasting him with former President Donald Trump.

“Joe Biden is the most pro-union president in American history, the first president to walk a picket line, the defender of more than 1 million pensions, and a champion for working people over greedy corporations,” a Biden campaign spokesperson said. “That’s why our campaign has more than 30 unions supporting us — it reflects Joe Biden’s record of delivering results for working families while Donald Trump delivers for his wealthy donors and himself.”

The concerns are part of growing anxiety among the Democratic Party and its allies about Biden’s candidacy. Senate Majority Leader Chuck Schumer told Biden in a private conversation last Saturday that it would be best if he dropped out of the 2024 presidential race, ABC News sources previously reported. House Minority leader Hakeem Jeffries is said to have expressed a similar sentiment, ABC News found.

To be sure, Biden retains support from many of the nation’s largest labor unions. The AFL-CIO, a labor federation that boasts about 12.5 million members, told ABC News that it stands by a statement issued last week reiterating its support for the Biden-Harris ticket.

“We are still Riding with Biden,” DeLane Adams, assistant communications director at the 600,000-member International Association of Machinists and Aerospace Workers, an affiliate of the AFL-CIO, told ABC News.

Several other unions echoed that ongoing support for Biden’s presidential bid, including the Communication Workers of America and the International Union of Painters and Allied Trades.

The UFCW, the 1.3-million member union to which Local 3000 belongs, shared a statement with ABC News on Friday pledging its continued support for Biden’s presidential campaign.

“President Biden is the nominee of the Democratic Party and the only pro-labor candidate in this race, and we strongly support his candidacy over former President Trump,” the UFCW said.

Larry Cohen, former president of the Communications Workers of America, said Biden will ultimately decide whether to continue his campaign. If union leaders were to speak out publicly, they may “damage his chances to beat Trump,” Cohen added. “They’re playing a tricky risk game.”

Still, he said, if Biden steps aside, union leaders would likely come out in support of Vice President Kamala Harris as the nominee. The two labor leaders who spoke to ABC News agreed. “It has to be the vice president,” one labor leader said, citing the limited time remaining before Democrats nominate their presidential candidate.

At least one prominent figure in the Democratic party has voiced concern about whether unions would sustain the same level of backing for an alternate candidate. Speaking on Instagram Live on Thursday, Rep. Alexandria Ocasio-Cortez, D-NY, who has supported Biden’s bid, said labor unions may not back a replacement to the same degree as they would Biden.

“Whether people like it or not, President Biden has very strong, broad union support, and that is not something that just goes automatically to any Democrat.”

Cohen said such fears are overstated due to the severity of the threat Trump poses for workers and unions. “Another four years of Donald Trump would be worse than the first,” Cohen said. “The key difference is Trump versus Biden or Trump versus Harris, not Biden versus Harris.”

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