It sounded like a potent combination: unions and other progressive groups teaming up to form a new Super PAC aimed at defeating Donald Trump. The PAC, called For Our Future, was organized by four major labor groups, who hoped to raise $50 million for voter-turnout efforts: the AFL-CIO; the American Federation of State, County and Municipal Employees; the American Federation of Teachers; and the National Education Association. Environmental activist Tom Steyer, who’d reportedly been discussing a collaboration with the AFL-CIO for several months, announced that he would give $5 million to the group.

Then, last week, The New York Times published a pair of letters sent to AFL-CIO president Richard Trumka by the presidents of seven construction unions who were “enraged” by Steyer’s participation. The unions would not support the PAC, their leaders wrote, and they asked the AFL-CIO to sever its ties to Steyer. The Times framed the conflict as a “rift between labor and environmentalists” that could derail the Democrats’ voter-mobilization efforts in the fall. But the letters amount to more of a public airing of preexisting, internal disagreements within the AFL-CIO than evidence of a green-labor split. As the partnership with Steyer indicates, labor groups and environmentalists are finding more common ground than ever—leaving unions allied with the fossil-fuel industry increasingly isolated.

The letter from the building trades organizations warns that the AFL-CIO has been “infiltrated by financial and political interests.” Those same unions, however, have nurtured their own relationships with special interests—notably the American Petroleum Institute, the largest trade association for the oil and gas industry. Letter signatory Sean McGarvey, the president of the AFL-CIO’s Building and Construction Trades Department, also co-chairs the Oil and Natural Gas Industry Labor-Management Committee (OGILMC), which he describes as “a unique partnership between America’s Building Trades Unions and the American Petroleum Institute.”

The partnership was founded in 2009 to promote domestic oil and gas production. As of 2012, the API had poured over $2.6 million into the group, with at least another $85,000 going directly to the AFL-CIO’s Building and Construction Trades Department. In early April, McGarvey appeared at an API conference on pipelines; less than two weeks later, API chief executive Jack Gerard spoke at the Building Trades Unions’ legislative conference, an event the API has sponsored.

The Laborers’ International Union of North America (LIUNA), whose president, Terry O’Sullivan sent a separate and more dramatic letter to Trumka, is also an OGILMC member. LIUNA considers the API an “employee partner,” and the lobby group has provided financial backing for some of the union’s events. Last year, the API relaunched its “Vote4Energy” program, which backs candidates who support expanded oil and gas extraction; O’Sullivan spoke on a panel at the launch event. “We need to have a rational and thoughtful conversation about energy in this country. It’s not oil that’s dirty—it’s politics,” he said. (LIUNA did not return requests for comment.)

The alliance between the building-trades unions and the API was on full display in the public debate over the Keystone XL pipeline, which both supported. In 2012, LIUNA dropped out of a coalition of labor and environmental groups called the BlueGreen Alliance (which included nine AFL-CIO member unions) because the coalition opposed the pipeline. O’Sullivan used strong language reminiscent of his more recent letter to express disagreement with the Steelworkers, the SEIU, CWA, UAW, and other unions who’d joined the Sierra Club and Natural Resources Defense Council, writing that he was “repulsed by some of our supposed brothers and sisters lining up with job killers.” At the time, unemployment within the construction industry was well above the national average, and rising.

Steyer was on the other side; he used his influence as a major Democratic donor to elevate an unlikely campaign against the pipeline into a high-profile political battle. Clearly, the construction unions have not forgiven the billionaire for helping to squash a project they saw as a source of jobs. O’Sullivan, in his letter to Trumka, referred to Steyer as a “job-killing hedge fund manager with a bag of cash.”

“Certainly the division over the Keystone XL pipeline is an important piece of the background to this story,” says Jeremy Brecher, a labor historian and co-founder of the Labor Network for Sustainability. (Brecher is also a Nation contributor.) But it’s not the whole story. Several of the unions who’ve objected to cooperation with Steyer—including LIUNA—have already endorsed Hillary Clinton, who announced her opposition to Keystone last year.

Also provoking the pushback is a shift within the labor movement on climate and energy issues. The AFL-CIO opposed the 1997 Kyoto protocol, and did not endorse emissions reductions targets laid out by the Intergovernmental Panel on Climate Change. The labor federation started to engage more substantively with climate change in late 2006, when it formed an energy task force and declared that “human use of fossil fuels is undisputedly contributing to global warming, causing rising sea levels, changes in climate patterns and threats to coastal regions.” But according to Brecher, the energy task force was dominated by representatives from mining and construction unions, who “insisted on an ‘all of the above’ energy policy that included coal, nuclear, oil and natural gas as necessary for jobs and economic development.”

Under Trumka, the AFL-CIO has grown more open to alliances with other progressive organizations, including climate groups. That strategy was controversial within the federation before Steyer and For Our Future PAC came into the picture. But now advocates for “all of the above” are more isolated, within both the Democratic Party and organized labor. “The labor movement, like the rest of American society, has increasingly recognized the reality of climate change and the need to address it, and that has gradually eroded the control those [fossil fuel- friendly] unions exercise over energy and climate policy,” says Brecher. The letters to Trumka hint at this loss of influence. “[A] growing trend within the Federation seem to consistently minimize the importance of Building Trades jobs and our members’ livelihoods in the pursuit of a coalition strategy,” the construction unions wrote. (The AFL-CIO declined a request for comment.)

That the AFL-CIO was willing to partner with Steyer at all is a sign that the gulf between labor and the climate movement is narrower than it once was. The federation has called Obama’s Clean Power Plan an “historic step,” and in December, the federation issued a statement of support for the climate agreement reached in Paris. As with the alliance with Steyer, these developments were not greeted with uniform enthusiasm across the AFL-CIO’s membership. But the member unions that do remain strong proponents of domestic fossil fuel production represent only a portion of the AFL-CIO’s members. “Their concern that their policy has become really a marginal view is certainly part of what they’re trying to push back against here,” Brecher says. “There’s now really a public presence in organized labor and across the labor movement in many different unions to promote climate protection, and jobs through climate protection.” (A number of examples are detailed here.)

Even many of the same unions who’ve balked at the idea of working with Steyer are taking advantage of jobs in the renewable energy sector. The United Association of Plumbers, Fitters, Welders, and Service Technicians describes the “green” sector as “one of the fastest growing sectors in our industry right now, and the UA drives “green training trailers” around the country to demonstrate energy-efficiency systems. LIUNA applauds the recent expansion of renewable-energy standards in California because they “created thousands of jobs in construction including many opportunities for LIUNA members.” As it happens, Tom Steyer supported the stricter renewable mandate, too. So, while Terry O’Sullivan might not be ready to work with a “hedge fund manager with a bag of cash,” he has more in common with Steyer than his letter suggests.