A pair of Democratic groups will team up to fund a new super PAC that will devote millions of dollars to electing top-tier Democratic Senate candidates in swing states.

The League of Conservation Voters Victory Fund and United Steelworkers Works have formed a new super PAC, New American Jobs Fund, devoted to voter persuasion and mobilization efforts in support of Democratic Senate candidates in Pennsylvania, Nevada, Ohio and North Carolina.

The groups have committed nearly $4 million to the effort, which marks a rare partnership between two wings of the Democratic base. And it is yet another sign of the growing influence  of environmental groups in electoral politics.

“The Jobs Fund brings together conservationists and labor to elect the right leadership to Congress, helping us build a clean-energy economy, creating jobs in America while also protecting our clean air and combating climate change,” said LCV President Gene Karpinski. “Through this new partnership, we will fight for America’s middle class by working to elect forward-thinking leaders who know we don’t have to choose between good jobs and a clean environment — we can and must have both.”

The efforts will benefit Senate candidate Katie McGinty, Nevada Senate candidate Catherine Cortez Masto, North Carolina Senate candidate Deborah Ross and Ohio Senate candidate Ted Strickland.

The announcement also comes as national Democratic groups have begun reassessing their spending priorities, pulling funding for television ads in Strickland's race as his opponent, Republican Sen. Rob Portman, seems to be regaining his footing.

Earlier this week, LCV announced an $860,000 ad buy in the Nevada Senate race.

Democrats still hold out hope of regaining a Senate majority. And nearly all of these races are keys to those ambitions.

By joining forces, labor and environmental groups are also signaling that if Democrats regain control of the Senate, they intend to team up on legislative priorities, including defeating the Trans-Pacific Partnership trade pact.

“Clearly, control of the U.S. Senate is in play, and this effort to directly communicate with tens of thousands of voters in these key states could well have an impact on the outcome of the election," said United Steelworkers International President Leo W. Gerard. "We are proud to continue this partnership that we feel is necessary to take our message to the voters.”