The Sierra Club launched a week-long advertising campaign Monday to slam Sen. Mark Kirk (R-Ill.) for voting to scrap the Environmental Protection Agency’s (EPA) climate rule for power plants.

The environmental group started its “aggressive” campaign with a full-page ad in the Daily Herald, circulated in Chicago’s suburbs.

It accuses Kirk of voting three times “to put big polluter profits before the health of Illinois families,” and urges readers to tell Kirk to “stop attacking clean air” and “support the Clean Power Plan.”

Kirk is running for reelection and is one of the GOP’s most vulnerable senators. The Sierra Club’s campaign does not advocate voters to support or oppose him, so it is not treated as a campaign ad for legal purposes.

“Sen. Mark Kirk voted repeatedly against the health of Illinois families by attacking the Clean Power Plan, the first ever steps to limit carbon pollution from dirty, coal-fired power plants” Liz Perera, the Sierra Club’s climate policy director, said in a statement, adding that the majority of people in Illinoi support the regulation.

“Sen. Kirk needs to stand with his constituents, not with the polluters that are hurting their health,” she said.

The Sierra Club’s campaign comes a week after the League of Conservation Voters launched its own ads against Kirk.

Kirk, once an ally to greens, is now a top target for them, after moves that they say turned him against climate and environmental policies.