One of the largest labor unions in America is seeking to present its case to both major political parties before making a presidential endorsement.

Sean O’Brien, general president of the Teamsters Union, has signaled to allies in both the Republican and Democrat parties that he would like to speak at each of their conventions this summer before announcing whom the massive union will support for president.

It has been more than 20 years since the 1.3-million-person union was represented at both the Republican and Democratic national conventions. It has been 36 years since the Teamsters endorsed a Republican, when leadership backed George H. W. Bush for president in 1988. The union has backed every Democrat presidential candidate since then except for in 1996 when the union abstained from endorsing Clinton or the Republican Bob Dole.

O’Brien’s desire to speak to Republicans highlights a growing rift between O’Brien and vocal Teamsters members who recoil at the thought of supporting former President Trump.

Teamsters Vice President At-Large John Palmer recently told CNN that Trump has been “anti-union for decades.” Palmer added that he believes the Teamsters are “wasting time” by entertaining both sides and not actively backing President Biden.

Trump has attempted to persuade the major unions to support his reelection bid but his overtures have failed to materialize into concrete endorsements. Although Trump visited the United Auto Workers picket line in September of 2023, UAW leadership chose to endorse Biden in January 2024.

Kara Deniz, a Teamsters spokesperson who confirmed O’Brien’s outreach to both parties, told NBC News that the union’s members’ “voices will be heard, regardless of party.”

“Rank-and-file members will be on the ground and active in both conventions this year to make sure elected officials know the Teamsters’ issues and are hearing the challenges that working people face in this country,” Deniz said. 

O’Brien, elected in 2022 on a wave of reform inside the union, has shown an interest in speaking more broadly to diverse political groups during the 2024 election cycle. The Teamsters have already held roundtable discussions with independent presidential candidates Robert F. Kennedy Jr. and Cornel West. 

But it was O’Brien’s meeting at Mar-A-Lago with Trump in January of this year that ruffled the feathers of the union’s more progressive members. A last-minute endorsement for Trump could prove costly to Democrats in union-dense swing states such as Wisconsin, Michigan, and Pennsylvania.

Republicans will hold their convention in Milwaukee this July, while Democrats will hold theirs in Chicago in August. Following the news on Monday, Kevin Munoz, a spokesman for the Biden campaign, refused to confirm whether the Democrats will grant O’Brien a speaking slot in Chicago.