Sen. Ron Johnson (R-Wis.) said in an email blast Tuesday that a green group is on an “environmental jihad” against him.

The broadside came in response to a new ad campaign from the League of Conservation Voters (LCV) that criticizes Johnson for questioning climate change.

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“The League of Conservation voters is not an organization with a balanced approach to a cleaner environment,” states the email from the Johnson campaign. “They are an extreme left group on an environmental jihad.”

The email, which also solicited donations from supporters, denounced what Johnson said was an “unholy
alliance” between LCV and the Obama campaign that gives the green group
“unlimited resources and campaign expertise.”

The environmental group on Monday announced it would target Johnson and three GOP House members in a $2 million campaign.

The campaign is directed at what LCV spokesman Jeff Gohringer called the “anti-science, anti-climate wing of Congress.”

Johnson’s campaign blasted the environmental and emissions regulations that the league supports. Like most GOP lawmakers, Johnson says those rules will damage the economy.

“They are declaring political war and they’ll do or say anything to defeat me,” Johnson said. “I need to be able to respond to their attack ads with the truth. I can’t allow their negative smears to stand unopposed.”

Johnson, who isn’t up for reelection until 2016, disputes the existence of man-made climate change.

Many Republicans deny or are skeptical of the link between climate change and human activity, while others say they believe human activity factors into climate change but are unsure of the extent.