Two environmental groups are up with a major ad buy slamming Rep. Jason Altmire's (D-Pa.) environmental record, a move that could hurt the centrist Blue Dog Democrat with some in the Democratic base in his suburban Pittsburgh district.

The League of Conservation Voters and NRDC Action Fund are behind the ad.

"Altmire sided with corporate polluters and voted to block new safeguards to keep mercury and other dangerous substances from our air even though nearly one in ten women in our region have mercury levels high enough to risk their babies’ health," the ad's narrator claims as images of a concerned-looking pregnant woman are interspliced with shots of Altmire and smokestacks.

Altmire's campaign fired back hard. "Once again, a Washington, D.C.-based special interest group has come into western Pennsylvania to saturate the airwaves with negative attack ads highlighting my unwillingness to go along with the EPA's unrealistic and heavy-handed attempt to impose burdensome new regulations," he said in a statement.

"These regulations would dramatically raise our electricity rates and make it impossible for local energy producers to compete economically and to continue employing thousands of western Pennsylvania workers," Altmire continued. "I represent 700,000 residents of western Pennsylvania and live here myself, along with my family. To imply that I would support any legislation that would promote an unhealthy environment and pollute the air we breathe and the water we drink is preposterous."

The ad, which has $350,000 behind it, is running on broadcast and cable television. Altmire is facing a threat from redistricting and may be forced into a tough race by the Republicans who are redrawing his district's lines. He and Rep. Mark Critz (D-Pa.), another centrist Democrat, may face off, and he could have a tough general election as well if Republicans make his swing seat any more conservative.

The region heavily relies on coal and steel, making it unlikely Altmire will change his voting habits on environmental issues. But in an already tough political environment, ads that could hurt him with the area's liberal base are nothing but bad news for the congressman.

Watch the ad here:

This post was updated at 6:33 p.m.