One of America’s most influential unions, the International Brotherhood of Teamsters, has refused to endorse the U.S. president for the first time since 1996.

The union, which has about 1.3 million members in the U.S. and Canada, said it had received “few commitments on key Teamsters issues” from both Democratic candidate Kamala Harris and Republican candidate Donald Trump.

The party also claimed that polls among its rank-and-file members had shown “no definitive support” for either candidate, even though two recent polls showed a skewed balance of support for Trump.

The move is a major setback for Harris’s efforts to win over working-class voters with less than 50 days to go until election night.

This show of support could mobilize thousands of Teamsters who live, work and vote in the crucial states of Pennsylvania, Michigan and Wisconsin.

Shortly after the announcement, several regional Teamsters councils, which represent more than half a million members in Michigan, Wisconsin, Nevada and California, indicated they would support Harris.

In a statement, Harris’ campaign stressed that she supports “the overwhelming majority of unions” and noted that many Teamster locals support her candidacy.

“While Donald Trump says striking workers should be fired, Vice President Harris has literally spent her entire career on the picket line supporting unions,” said campaign spokesperson Lauren Hitt.

The union’s members, a coalition of truck drivers, warehouse workers and pilots, have long been considered politically diverse.

General President Sean O’Brien has tried to reach out to Republicans since taking over the executive branch in 2022.

He has reached out to more populist figures within the party, such as U.S. Senators Josh Hawley of Missouri and J.D. Vance of Ohio, who is now Trump’s running mate.

In January, O’Brien also met privately with Trump at his Mar-a-Lago estate, shortly before the former president attended a roundtable discussion with the union’s leadership at its headquarters in Washington, DC.

After that meeting, Trump said he believed he had a “good chance” of getting the union’s support.

The board also spoke with President Joe Biden before he stepped down as the Democratic nominee, and with third-party candidates Robert F. Kennedy Jr. and Cornel West.

But the union alarmed Democrats when it made its first financial contribution to its opponents in years, donating $45,000 (£34,000) – the maximum allowed – to both the Democratic and Republican National Party Conventions in February.

Mr. O’Brien was also the first Teamster leader to ever speak at the Republican National Convention (RNC).

When invited to speak at the event in Milwaukee, the labor leader praised Trump as “a tough guy” but declined to endorse him.

He later also criticized Trump and his top campaign manager and billionaire businessman Elon Musk for comments in which the two discussed firing workers who threatened to go on strike.

After deciding to speak at the RNC, Mr. O’Brien did not receive an invitation from Democrats to address their convention last month.

Instead, the party invited members to represent the organization and speak from the stage of the party conference.

Some Teamsters members have expressed anger at Mr. O’Brien for his right-wing approach.

Last month, the Teamsters National Black Caucus and six local union chapters defied national leadership by taking the initiative to endorse Harris and call on their members to support her.

On Monday, Harris held a long-awaited roundtable with the Teamsters leadership that lasted an hour and a half.

A New York Times article described the meeting as “tense at times,” but a Teamsters spokesman disputed that characterization when asked by the BBC.

During their meeting, the Times added, Harris told the Teamsters leaders: “I’m confident I’m going to win this. I want your support, but if I don’t get it, I’m going to treat you exactly as if I had your support.”

Speaking to reporters after Harris delivered her statement, O’Brien noted that there was “not that much difference” between the answers she and her predecessor Biden had given.

Biden has frequently described himself as “the most pro-labor president ever,” citing policies that have made it easier for American workers to organize and prioritized unionization on federal government projects.

Last September, he made history as the first U.S. president to walk a picket line when he joined the United Autoworkers in Michigan in a strike against the three major U.S. auto companies: General Motors, Ford and Stellantis.

The Biden administration has also bolstered the Teamsters’ pension fund by $36 billion, a move the administration says has prevented more than 600,000 members from having their pension incomes cut.

Mr. O’Brien and other leaders have also acknowledged on several occasions that Biden is “great for unions.”

But before he left office in July, some reports suggested the Teamsters had no plans to support Biden’s bid for re-election.

Correction: An earlier version of this story was updated to reflect that the Teamsters are the fourth-largest union in the United States, but not the largest.

On Wednesday, prior to announcing that it would not endorse either Harris or Trump, the union released polls of its members.

In an electronic poll conducted after the RNC, 59.6% of Teamsters members voted in favor of the union’s support for Trump, compared to 34% for Harris.

A separate poll conducted last week found Teamsters again supporting Trump by a lopsided margin: 58% to 31%.

Despite these results, the union said in a statement that an extensive poll of members found there was no majority for Vice President Harris and no universal support among members for President Trump.

Trump’s campaign immediately praised the polls on Wednesday.

“While the Teamsters leadership has not made a formal statement of support, the hardworking members of the Teamsters have made it loud and clear that they want President Trump back in the White House,” said Karoline Leavitt, campaign spokesperson.