The leader of one of the nation’s oldest and largest unions stunned political observers by issuing a surprise endorsement for a Senate Republican stalwart over the weekend.

Teamsters General President Sean O’Brien, who famously nearly came to blows with now-Secretary of Homeland Security Markwayne Mullin during a Senate hearing before ultimately becoming acquaintances, issued a ringing endorsement of Sen. Ashley Moody, R-Fla., signaling a major break from national union sentiment that has tended to favor Democrats.

"Just voted in the State of Florida for the first time, and very proud to have cast a ballot for Sen. Ashley Moody," O’Brien, whose 123-year-old union is about 1.3 million-strong, announced Sunday.

5 TAKEAWAYS FROM FLORIDA SENATE PRIMARY: GOP SEN ASHLEY MOODY WILL FACE DSA'S NIXON "Sen. Moody has been extremely helpful working with the Teamsters to protect workers’ pensions, defend good-paying jobs, and support well-funded union apprenticeship programs."

"The Teamsters look forward to working with Sen. Moody in her role on the Senate HELP Committee to pass the Faster Labor Contracts Act and get this critical legislation signed into law to protect American workers," he added.

FRUSTRATED BLUE-COLLAR UNION BOSSES RIP SOCIALIST POLITICIANS, WARN OF LABOR EXODUS FROM DEM PARTY O’Brien, a self-described "lifelong Democrat," previously spoke at the 2024 Republican National Convention, but emphasized at the time that the Democratic Party had snubbed his request to speak at its convention.

"If the far-left want to criticize me and attack me, that’s OK. If the far-right wants to do the same, that’s great. I represent 1.3 million hardworking men and women," O’Brien said at the time. Fox News Digital reached out to the Teamsters as well as Moody’s campaign for comment.

Moody, a former state attorney general, said in a statement that she was proud to have O’Brien’s endorsement: "I’ll always fight to protect hardworking Americans, strengthen good-paying jobs, and ensure resources are available to train our next generation. It’s been great to deliver for Florida’s working families," she said.

After O’Brien endorsed Moody, the lawmaker’s Democratic opponent responded by posting a photo she once took with O’Brien and writing that "Ashley Moody never walked the line with you." "But ok brother.

Shout out to all the rank and file Teamsters that are voting for me. I will always stand with you," Democratic nominee Angie Nixon, a state lawmaker from Jacksonville whose platform is considered DSA-aligned, wrote on O’Brien also caught heat for voting in Florida, which appeared to signal a move from his hometown of Boston.

"Be union leader — move to a famously anti-union state — vote for a famously anti-union candidate — Brag about it — really cool stuff man," a top commenter on O’Brien’s post said. Other critics characterized O’Brien as a "scab", union jargon for someone who crosses a strike picket line to return to work for the company with which they are at odds.

The Teamsters leader’s announcement marked a noteworthy development with polls set to open nationwide in a matter of hours.