Actor Leonardo DiCaprio is filming in Washington and tweeting about a Senate amendment addressing greenhouse gas regulations.

The amendment is expected to come to the floor soon for a vote.

And DiCaprio tweeted Wednesday: We need #cleanair but the US #Senate may vote 2 allow for air pollution. Tell your Senators NO DIRTY AIR Call: 1-877-573-7693 #fb

DiCaprio urged his followers to call an activist hotline that connects callers with their senators and coaches them on how to urge lawmakers to vote no. The vote in question, which could happen as soon as Wednesday but might happen later in the week, is for an amendment introduced by Senate Minority Leader Mitch McConnell (R-Ky.) to the small-business bill that would essentially block the Environmental Protection Agency from regulating greenhouse-gas emissions.

The Republican amendment to the small-business bill is part of a wider ongoing fight over EPA climate policies and funding. This month, a group of Democrat senators, including key members of the leadership such as Majority Whip Richard Durbin (D-Ill.) and Barbara Boxer (D-Calif.), protested that Republicans are drastically cutting funding to the EPA and threatening to “undermine the nation’s landmark environmental laws.”

DiCaprio, best known for his star-making role in the 1997 movie Titanic, is in Washington filming a movie based on the life of legendary FBI director J. Edgar Hoover. He is typically concerned with activist causes in his tweets and has been a longtime supporter of the environment.