By Laura Barron-Lopez - 07/22/14 01:36 PM EDT
The Environmental Defense Fund is hitting Republican Senate candidate Rep. Cory Gardner (Colo.) for donations from the oil and gas industry.
The 30-second TV ad buy will run across Colorado for two weeks starting Tuesday and costs $400,000.
"Now out-of-state oil billionaire Koch brothers are funneling in millions attacking [Sen.] Mark Udall [D-Colo.], that's just not the Colorado way.
According to a Wall Street Journal piece, oil and gas companies shifted their contributions from Udall to Gardner, after Gardner announced his plans to challenge the incumbent earlier this year.
Between the first and second quarter filings, industry contributed $223,600 to Gardner and $41,460 to Udall, according to the Center for Responsive Politics, the Journal reports.
The tight race could boil down to energy, issues as Democrats argue over initiatives that ail will likely make the November ballot, which seek to restrict fracking for natural gas in the state.