The Teamsters will not endorse Vice President Kamala Harris or former President Donald Trump in the 2024 election, marking the first time since 1996 that the group has not backed a candidate in a race for the White House.

For decades, the group has rallied behind Democratic presidential contenders, including Joseph R. Biden in 2020, Hillary Clinton in 2016, and Barack Obama in 2012.

However, the General Executive Board of the International Brotherhood of Teamsters announced Wednesday that the group was left “with few commitments on top Teamsters issues” from Ms. Harris and Mr. Trump. They said that rank-and-file truck drivers and warehouse workers were too divided over the two candidates for the union to pick a side.

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“Unfortunately, neither major candidate was able to make serious commitments to our union to ensure the interests of working people are always put before Big Business,” Teamsters General President Sean M. O’Brien said in a statement. “We sought commitments from both Trump and Harris not to interfere in critical union campaigns or core Teamsters industries — and to honor our members’ right to strike — but were unable to secure those pledges.”

The union also released a national electronic poll of its 1.3 million members, which found that rank-and-file members favored Mr. Trump over Ms. Harris by a 59.6% to 34% margin.

The survey followed a series of straw polls of roughly 300 Teamsters local unions conducted between April 9 and July 3 that showed President Biden had a 44.3% to 36.3% lead over Mr. Trump before he pulled the plug on his campaign.

Mr. O’Brien has a habit of ruffling feathers. He has knocked heads with Republicans on Capitol Hill. In July, he also turned some heads when he became the union’s first president to speak at a Republican National Convention.

“As the strongest and most democratic labor union in America, it was vital for our members to drive this endorsement process,” Mr. O’Brien said Wednesday. “Democrats, Republicans, and independents proudly call our union home, and we have a duty to represent and respect every one of them.

“We strongly encourage all our members to vote in the upcoming election, and to remain engaged in the political process,” he said. “But this year, no candidate for president has earned the endorsement of the Teamsters’ International Union.”