The head of the International Brotherhood of Teamsters gave a surprising boost to former President Donald Trump’s election effort on Monday, calling the GOP nominee “one tough SOB” in a speech at the Republican National Convention in Milwaukee.

Teamsters General President Sean O’Brien did not endorse Trump for the White House but praised him as a politician “not afraid” to hear from “new, loud, and often-critical voices.” He said his union would happily work with a GOP administration if given the opportunity.

“I refuse to keep doing the same things my predecessors did,” O’Brien said in a speech that at times criticized both Democrats and Republicans. “Today the Teamsters are here to say we are not beholden to anyone or any party.”

It was an unusual speech from a high-profile labor leader at the RNC.

Organized labor is a pillar of the Democratic Party and a crucial ally in President Joe Biden’s reelection plans. Most major unions have denounced Trump due to his vehemently anti-union and anti-immigrant record in the White House.

O’Brien had sought out the speaking invitation, upsetting Teamster members who back Biden. But he has defended the move as a bit of bipartisan political outreach. (O’Brien also dined with Trump — and posed for a thumbs-up photo with the former president — back in January.)

He brushed off criticism from union members and other progressive allies in his address.

“I don’t care about getting criticized,” he said. “It’s an honor to be the first Teamster in our 121-year history to address the Republican National Convention.”

The union has not yet made an endorsement in the presidential race, though it formally backed Joe Biden in his first run against Trump in 2020.

O’Brien took over as Teamsters’ president in 2022, succeeding longtime president James P. Hoffa, the son of Jimmy Hoffa. He led the union through its high-profile negotiations with logistics giant UPS last year, and made headlines by nearly coming to blows with a Republican senator during a hearing on Capitol Hill.

The vast majority of Republicans vote against organized labor’s interests when it comes to legislation in Washington, while most Democrats vote in favor. For instance, it was Democrats who shepherded an $86 billion pension bailout through Congress in 2021 to help the Teamsters and other unions, over the opposition of Republicans.

Yet O’Brien criticized both parties when it comes to helping workers.

“There are far too many people on both sides of the aisle still caught up in knee-jerk reactions to unions, who subscribe to the same tired claptrap that unions destroy American companies,” he said.

Trump, who was nearly assassinated at a campaign rally in Pennsylvania over the weekend, announced last month that he’d extended a speaking slot to O’Brien for the convention. The former president seemed to relish the validation of a high-profile union leader, saying on Truth Social that he and O’Brien together could “Make America Great Again.”

It was in reference to the assassination attempt that O’Brien on Monday called Trump “one tough SOB.”

Yet there’s been no indication that Trump, a hotel mogul who dealt with unions routinely in his businesses, would break with the anti-union labor policies of his first term.

As president, Trump stacked the National Labor Relations Board with pro-business appointees who consistently ruled against unions and workers, making it more difficult to organize workplaces. He also repealed a slew of wage and safety protections that labor groups had lobbied for, and tried to weaken collective bargaining for federal employees.

One high-ranking Teamster official has publicly criticized O’Brien for making the RNC appearance.

John Palmer, a union vice president at-large, wrote in an opinion piece last week that the speaking engagement “normalizes and makes the most anti-union party and President I’ve seen in my lifetime seem palatable.”

Several other labor leaders have come out forcefully against Trump.

Shawn Fain, the president of the United Auto Workers, called Trump a “scab” as he announced his union’s endorsement of Biden for reelection. And on Monday, Liz Shuler, president of the AFL-CIO labor federation, said in a statement that Trump would continue a “betrayal” of the working class if he were to return to the White House.

“Donald Trump has a miserable record of breaking every promise he’s made to working people,” Shuler said.