One of the nation's largest environmental advocacy groups is joining one of the nation's largest industrial unions to launch a multi-million dollar campaign to mobilize voters in key races that could decide the balance of power in the United States Senate.

The League of Conservation Voters (LCV) and United Steelworkers (UAW) announced Monday that they are committing $3.1 million to boost turnout in four states with pivotal Senate seats up this cycle: Arizona, Montana, Nevada and Ohio.

In Montana and Ohio, the campaign is designed to tout the environmental record of two incumbents up for re-election in 2018 in states that Donald Trump capture in the 2016 presidential election: Sen. Jon Tester and Sen. Sherrod Brown.

The campaign is also targeting two pickup opportunities for Democrats this cycle. The retirement of Sen. Jeff Flake gives Democrats in Arizona a chance to capture one of the state's U.S. Senate seats for the first time since 1988. While the state has not yet held its primary, Rep. Kyrsten Sinema is a heavy favorite to advance to the general election, and the campaign touts her as a "champion" on environmental issues.

In Nevada, GOP Sen. Dean Heller is the only Republican incumbent up this cycle in a state that Hillary Clinton won in the 2016 presidential election. Heller is taking on Democratic Rep. Jacky Rosen in November.

"We don’t have to choose between good jobs and clean air and water, and that’s why conservationists and labor are coming together once again to elect senators who share those values,” LCV President Gene Karpinksi said in a statement announcing the campaign, "We know that face-to-face conversations about what’s at stake bring voters to the polls, and our combined efforts will be key to retaking a pro-environment majority in the U.S. Senate that will invest in the clean energy jobs of the future and ensure that our health and safety take priority over corporate greed."

"Control of the U.S. Senate is in play, and this effort will directly communicate with the tens of thousands of voters who will decide the outcome of the election in these key states," United Steelworkers International President Leo Gerard added in a statement Monday.

The two groups had a similar partnership during the 2016 election, but in this election cycle they are getting involved "much earlier" to take advantage of an energized Democratic electorate, said LCV's Senior Vice President of Campaigns Pete Maysmith.

"We wanted to tap into that energy even earlier in terms of engaging with voters and with potential voters in those four states," Maysmith told ABC News.

Maysmith also said that while the campaign is focused on touting the overall records of the four Democrats running in these races, the messaging will vary from state to state where the joint campaign sees opportunities to target issues that voters in individual states care about.

"In Nevada we know that clean energy, solar and wind in particular, are absolutely popular issues with the voters, and they get that it's good for the economy" Maysmith said.

Public lands in Montana was another example of a local issue that Maysmith said "resonates with voters directly," and could mobilize them to the polls to re-elect a red state Democrat like Tester.