Former New York City Mayor Michael Bloomberg is paying to run negative advertisements targeting four state attorneys general for their legal actions against a key climate change rule.

Bloomberg’s advisers told The New York Times that the campaigns would cost more than $10 million, to defend President Obama’s regulation to slash carbon dioxide emissions from power plants.

The ads, through Bloomberg’s Independence USA PAC, target Pam Bondi of Florida, Bill Schuette of Michigan, Brad Schimel of Wisconsin and Chris Koster of Missouri. Koster is running for governor.

Bloomberg, who has been a billionaire media mogul since long before his term as New York’s mayor, has already spent a significant amount of his personal fortune fighting coal-fired power plants, which are expected to suffer greatly from the Environmental Protection Agency’s (EPA) rule.

Through Bloomberg Philanthropies, he has donated at least $80 million to the Sierra Club’s Beyond Coal campaign, which has claimed credit for helping a third of the country’s coal plant fleet close or announce closure since 2010.

Bloomberg also helps fund Everytown for Gun Safety, which campaigns for gun control measures and has a political arm that works to elect gun control-friendly candidates.

The attorneys general in Bloomberg’s crosshairs are among the 27 state attorneys suing in federal court to have the EPA’s climate rule overturned. They argue that the EPA does not have the authority to regulate in the way it is seeking to.

“These four attorneys general are trying to stop the president from doing something that I think is terribly important,” Bloomberg told the Times Friday. “I want the public to know what they’re doing. It’s very bad for everybody.”

“Independence USA PAC will not let these politically motivated attacks against the EPA stop the incredible progress that many states and communities are already making to reduce carbon pollution and increase clean energy use,” the group said on its website. “Our campaign hopes to expose the attorney general’s lawsuit for what it is — an ill-conceived attack on safeguards meant to ensure a clean, healthy and safe future for Americans all across the country.”