Many of America’s largest labor unions have now announced their endorsements of Kamala Harris’ presidential bid, as the vice president intensifies her campaign for the Democratic nomination.

Yet some notable union holdouts remain, suggesting Harris will still have some work to do to win over other working-class voters.

On Monday, the American Federation of Labor and Congress of Industrial Organizations (AFL-CIO), the biggest federation of unions in the U.S. and a longtime supporter of President Joe Biden, announced its endorsement of Harris.

“From day one, Vice President Kamala Harris has been a true partner in leading the most pro-labor administration in history,” said AFL-CIO President Liz Shuler. “At every step in her distinguished career in public office, she’s proven herself a principled and tenacious fighter for working people and a visionary leader we can count on. From taking on Wall Street and corporate greed to leading efforts to expand affordable child care and support vulnerable workers, she’s shown time and again that she’s on our side.”

Shuler added: “With Kamala Harris in the White House, together we’ll continue to build on the powerful legacy of the Biden-Harris administration to create good union jobs, grow the labor movement and make our economy work for all of us.’

Several other unions also have announced their support, including the Service Employees International Union (SEIU), the United Food & Commercial Workers International Union (UFCW), the American Federation of State, County and Municipal Employees (AFSCME) in addition to the American Federation of Teachers (AFT), the International Brotherhood of Electrical Workers and the United Steelworkers (USW).

The Biden-Harris administration has enjoyed the steady backing of union and labor groups over the past few years and it has sought to reciprocate. In his most high-profile show of support, Biden became the first sitting president to walk a picket line during the United Auto Workers’ strike against the Big Three automakers last fall.

But the UAW is one of the groups that has yet to announce its formal support for Harris’ White House bid. On Sunday, it issued a statement praising Biden’s leadership during his administration but stopped short of endorsing Harris.

‘The path forward is clear: we will defeat Donald Trump and his billionaire agenda and elect a champion for the working class to the highest office in this country,’ the statement read.

A UAW representative did not immediately respond to a request for comment Tuesday morning.

Republican nominee Donald Trump has sought to undermine UAW leadership, explicitly calling for the ouster of its head, Shawn Fain.

During his nomination acceptance speech in Milwaukee last week, Trump claimed, without evidence, that China was planning to build auto manufacturing sites in Mexico at the expense of assembly lines in the U.S.

“The United Auto Workers ought to be ashamed for allowing this to happen and the leader of the United Auto Workers should be fired immediately,’ Trump said, adding: ‘Every single autoworker, union and nonunion, should be voting for Donald Trump because we’re going to bring back car manufacturing and we’re going to bring it back fast.’

There remain dozens of automotive manufacturing plants in the U.S., many of which are in Southern states and the Midwest.

Trump has also sought to exploit the UAW’s concerns about the national transition to electric vehicles — something that caused the union to decline to explicitly support Biden’s 2024 candidacy.

“The federal government is pouring billions into the electric vehicle transition, with no strings attached and no commitment to workers,” Fain said last spring, according to CNBC. “The EV transition is at serious risk of becoming a race to the bottom. We want to see national leadership have our back on this before we make any commitments.”

The UAW has historically seen a steady 60-40 split between Democrat- and Republican-supporting members, according to Brian Rothenberg, a former UAW communications director and now a partner at Triumph Communications firm.

He said that while UAW members remain uneasy about the EV transition, there are other concerns about workplace safety, and especially the impact of Project 2025, a conservative blueprint that lays out actions to weaken public-sector unions.

‘That’s a much more robust issue for them than perhaps for the rest of the country,’ Rothenberg said.

UAW members have attended and participated in Trump events in Michigan, CNBC reported last year.

This past weekend, Trump and running mate JD Vance appeared at a rally in Grand Rapids, Michigan, to bolster support in the crucial swing state.

While UAW leadership has at least formally rejected Trump, another major union player has explicitly signaled its presidential endorsement is up for grabs.

Sean O’Brien, the head of the Teamsters Union, gave an impassioned speech against corporate interests at the Republican National Convention in Milwaukee last week that caused some commentators to question whether labor is now as fully united behind Democrats as they have traditionally been. 

‘I refuse to keep doing the same things my predecessors did,’ O’Brien said. ‘Today, the Teamsters are here to say we aren’t beholden to anyone or any party. We will create an agenda and work with a bipartisan coalition ready to accomplish something real for the American worker. I don’t care about getting criticized. It’s an honor to be the first Teamster in our 121-year history to address the Republican National Convention.’

A since-deleted post on X from the official Teamsters account in the wake of the speech appeared to signal internal rancor about O’Brien’s appearance.

“Unions gain nothing from endorsing the racist, misogynistic, and anti-trans politics of the far right, no matter how much people like Sen. Hawley attempt to tether such bigotry to a cynical pro-labor message,” the Teamsters account wrote on X, referring to the Republican senator from Missouri, Josh Hawley, then adding: “You don’t unite a diverse working class by scoffing at its diversity.”

In a statement, a Teamsters representative said the group has invited Harris to a roundtable discussion, and noted that its presidential endorsement are traditionally announced after the political parties’ conventions.

‘We are on our timeline and continuing to engage our members in this process,’ the spokesperson said.

The Democrats will host their convention in Chicago next month.

While Biden has been generally pro-labor, seeking to increase manufacturing jobs and improve workers’ bargaining power by banning noncompete agreements, active union membership has stayed on its historical downtrend during his term.

Yet even as Republicans have begun to pursue working-class and factory workers more aggressively, there is currently an effort underway to dismantle the National Labor Relations Board, the government body in charge of settling labor disputes.

The biggest backer of that initiative is Elon Musk, the head of Tesla, who has pledged his full support to Trump.

Musk, who earned praise from Trump at the Michigan rally, was sanctioned by the NLRB for tweeting in 2018: “Nothing stopping Tesla team at our car plant from voting union … But why pay union dues & give up stock options for nothing?”

More recently, Tesla became the subject of an NLRB complaint in May that accused the company of discouraging its employees ‘from forming, joining, or assisting the Union or engaging in other concerted activities.’ An initial hearing in that dispute is scheduled for this month.

A Tesla representative could not be reached for comment.