"Mr. President, we got a problem with labor."

The warning, delivered as Air Force One headed for Detroit last September, came from a trusted ally: Rep. Debbie Dingell, the Michigan Democrat who has known President Joe Biden for decades and prides herself on having her finger on the pulse of union halls. Initially, it landed with a thud.

"I am the most pro-labor president," Biden retorted, according to three people with direct knowledge of the exchange, as other members of Michigan's congressional delegation seated around a conference table on Air Force One nodded in agreement with the president.

"The presidents of the unions know it," Dingell said, according to the people. "Your workers in the halls don't."

By the time Air Force One landed in Detroit, the message seemed to have sunk in.

"The president heard me," Dingell said when asked about the exchange. "And the first thing he did when he got to the car show -- he went directly to the labor folks there."

"I tell you what, I don't screw around. Whatever she says, I do," Biden said as he took the stage at the auto show, referring to the congresswoman as "Commander Dingell." "But guess what? She's always right."

Dingell's message, delivered within two months of the midterm elections, was as much a warning about union support for the president as it was about broader crosscurrents of discontent and anxiety among some of the unions' rank-and-file -- with the companies they work for, with a changing economy and with Washington -- that she urged the president to be mindful of.

The 'most pro-union'

Ten months later, Biden already enjoys hefty union support for his reelection bid, including earning the endorsement of the AFL-CIO, which represents 12.5 million workers in 60 unions, and more than 20 other unions. And the White House points to a slew of pro-union policies embedded in signature legislation as evidence that Biden is indeed the "most pro-union president" in history.

But with the expiration of several major union contracts, the crosscurrents Dingell warned about are coming to a head in ways that risk upending the hard-fought economic progress for which Biden is only just beginning to loudly take credit. Absent an agreement, the United Auto Workers are threatening to go on strike in September; and the Writers Guild of America and Screen Actors Guild are already striking.

At least one major potential labor disruption was averted on Tuesday as the Teamsters reached a tentative agreement with UPS on a new contract to avert a strike by the union's 330,000 UPS employees next week. Just a 10-day UPS strike would have cost the economy $7.1 billion, according to an Anderson Economic Group estimate.

White House officials had repeatedly expressed confidence that UPS and the Teamsters, who resumed negotiations on Tuesday, would reach an agreement before their contract expires at the end of the month. The Biden administration was largely on the sidelines of the UPS-Teamsters dispute as Teamsters President Sean O'Brien specifically asked the White House not to get involved, but top White House officials kept in touch with both parties, including through backchannels, according to people familiar with the matter.

With one strike averted, the White House still faces the potential for more disruption in the coming months as the Hollywood strikes continue and a UAW strike looms on the horizon as early as mid-September. The stakes for the president are high: The spillover economic effects of multiple strikes converging at the same time could also be politically costly for the president, whose "Bidenomics" messaging increasingly ties his electoral fate to the health of the economy. Biden must also balance his desire to avert strikes that could prove costly for the economy with living up to his claim as "the most pro-union president" in history by standing by labor.

While Biden enjoys hefty union support, he has also faced lingering mistrust and concern among some of the rank-and-file of the Teamsters and UAW, according to people familiar with the dynamics, a perception fueled in part by the president's intervention to avert a freight rail strike in December.

"I think that a lot of rank-and-file people -- in the Teamsters, in the UAW -- are wary of politicians getting involved, stopping them from using their leverage to get the kind of contract where they can breathe," said former Democratic Rep. Andy Levin, who now serves as a distinguished senior fellow at the Center for American Progress.

While Biden had a unique authority to intervene in that case, Levin said the president's decision to intervene in the rail strike fed that perception.

Senior administration officials call the perception that Biden will intervene to stop a non-rail strike misguided, noting that Biden's intervention in December reflected the unique and critical role of freight rail and relied on statutory authority under the Railway Labor Act, which could not be applied to any of the looming potential strikes.

Asked whether Biden has ruled out intervening to stop a strike, Biden's top labor adviser Celeste Drake noted that the president "has not intervened in any strike under National Labor Relations Act" but would not take future action entirely off the table.

"The president believes that collective bargaining is the best way for workers and employers to reach a mutually beneficial agreement, and he respects the right to strike," Drake said.

The White House has also sought to defuse tensions with the UAW and its insurgent new president, Shawn Fain, who took the helm of the union in March after pledging a more confrontational approach to negotiations with auto manufacturers. Fain has criticized the administration for doling out electric vehicle subsidies without demanding union protections and has so far withheld the UAW's endorsement in the 2024 presidential election.

When Fain and other UAW leaders went to the White House last week to brief staff on their position, Biden asked to meet privately with the UAW president, according to senior administration officials, and the two spoke one-on-one in the Oval Office.

A senior administration official said Fain is also taking a "tough approach" to negotiations because he sees the transition to electric vehicles as a "critical moment for his workers."

By and large, the tensions between the UAW and the White House are policy-based and White House officials are working with the UAW to fine-tune the implementation of the Inflation Reduction Act's clean energy provisions to address some of the union's concerns, according to administration officials. The senior administration official said they have "opened up a constructive dialogue" with the UAW.

"The president's focus and connection and public commitment and outreach to union labor is like something I've never seen," said Gene Sperling, a senior adviser to Biden who is serving as his point person in the labor negotiations between the UAW and auto manufacturers. "You can have a strong relationship with a major constituency and still have challenges you have to keep your eyes open for."

"We don't always agree with everyone we consider friend or family or ally," another senior administration official said.

Marty Walsh, Biden's former labor secretary, argued "no union should have distrust in this administration," pointing to pro-union provisions embedded in the Bipartisan Infrastructure Law and Chips and Science Act that he says "will and have benefited members of organized labor."

The economic moment

White House officials and labor activists also see the convergence of labor negotiations across industries as the byproduct of a strong labor market, a post-pandemic economy in which workers want more say and the administration's persistent support for collective bargaining.

The pandemic also led to a cultural transformation of how Americans view work and their workplace -- and unions' place in it. According to Gallup's 2022 Work and Education survey, 71% of Americans approve of labor unions -- up from 64% before the pandemic, and the highest since 1965.

"You can sense there's more hunger and passion among the labor community for engaging in the kinds of confrontations with corporate power that are needed," said Faiz Shakir, the executive director of More Perfect Union and Sen. Bernie Sanders' former presidential campaign manager. "If you're a pro-union president, you have a unique ability to shape the conscience of these fights."

And as Biden seeks a second term, the White House is making the bet that standing with labor could reap political benefits.

Sixteen million wage and salary workers were represented by a union in 2022, according to the latest data from the Bureau of Labor Statistics.

And Biden's electoral map could be directly dependent on a handful of union-friendly battleground states: Michigan (15.3%), Pennsylvania (13.6%), Ohio (14.0%) and Nevada (12.8%) each have union membership rates higher than the 2022 national average of 10.1%, per BLS data.

Those union workers are also more politically engaged: According to a study of union impact on voter participation from the Harvard Kennedy School's Ash Center for Democratic Governance and Innovation, union members are "at least 3--5 percent more likely to vote."

Walking the labor walk

Since taking office, Biden has made repeated and concerted efforts to burnish his labor credentials. On Inauguration Day, one of his first acts as president was to fire the Trump-appointed National Labor Relations Board general counsel Peter Robb, an important signal to unions. A month later, he posted a video on social media expressing support for Amazon workers seeking to unionize in Alabama. He's made union support a key priority in multiple State of the Union addresses, and after announcing his 2024 reelection bid, Biden's first political stop was to a legislative conference for North America's Building Trades Unions.

And he's held meetings with organizers, including representatives from Starbucks and Amazon unions in May 2022 and a meeting with young organizers last week at the White House.

Biden has "given a signal to workers that he's on their side and they should have a real piece of the pie and they should have obtained the American Dream that has been so elusive over the last few decades," said D. Taylor, International President of UNITE HERE, which represents 300,000 workers across the hospitality, manufacturing, transportation, gaming, transportation, and other industries.

At last week's meeting, Biden joined Sanders, acting Labor Secretary Julie Su and top aides, including National Economic Council director Lael Brainard and Intergovernmental Affairs Director Tom Perez, for a conversation on unionizing with a group of young organizers reflecting the evolving face of the nation's unions. They work at entities like Sega, Starbucks, eBay, and higher education.

Attendee Ritu Acharya, a bargaining committee member for Local 33 Unite Here, a union of graduate teachers and researchers at Yale University, told CNN the group shared their challenges in organizing as Biden and Sanders sought to hear more about their experiences.

"We need better working conditions. We need better pay. We need fair treatment in our workplaces. We need a seat at the table, right? And so I think the administration, it seems to me from the fact that they were listening to us yesterday, they were appreciating the importance of workers in our economy," Acharya said.

Other attendees who spoke with CNN maintained that they're pleased with the president's engagement but stressed that they expect Biden to keep pressure on corporate America moving forward.

"I think there's a lot of public discourse about building the middle class and doing that, is supporting workers and having strong unions and having a strong NLRB," said Graciela "Gracie" Nira, a Starbucks employee and organizer with Starbucks Workers United.

"That language is in sync with what we're asking for and what we need, and it's strengthening and emboldening to hear that that as an economic framework or aspiration and feeling we can be an active part in making sure that happens," Nira added.

As the White House seeks to balance economic concerns with its support for union labor, union leaders are optimistic that the American people are on board.

"The American people are very supportive of workers fighting back. ... I think people fundamentally understand that the economy does not work for all right now and the unions are one of the ways to rebuild the middle class," said Taylor. "Workers have been inspired by the president and his position on unions -- that it is time to stand up. It is their time, and they have an administration that will be supportive of them."