Conservation Voters take aim at Gardner with new ad

The League of Conservation Voters will spend $1 million on an ad campaign attacking Republican Rep. Cory Gardner’s ties to the oil and gas industry in his challenge to Democratic Sen. Mark Udall.

The group announced the ad buy in a news release Thursday, saying they’ve added Gardner to their “Dirty Dozen” campaign targeting congressional candidates. Gardner is the first Senate candidate added to the list.

UPDATE: Gardner’s campaign responded with an email asking Udall to return campaign contributions from “anti-energy” groups.

The Conservation Voters ad buy is the latest in a series as the GOP tries to take over the U.S. Senate.

Freedom Partners and Americans for Prosperity, groups funded by the Koch brothers, have run ads attacking Udall on Obamacare.

The Senate Majority PAC countered with ads opposing Gardner.

As part of the buy, 156 ads will run on KMGH Channel 7 during April and May for $170,400, according to a contract filed with the FEC.

The League of Conservation Voters spent almost $900,000 in Sen. Michael Bennet’s narrow 2010 victory over Weld County District Attorney Ken Buck. In that race, outside groups spent about $30 million.