The American Energy Alliance is spending more than $400,000 on a new ad accusing Sen. Mark UdallMark UdallElection autopsy: Latinos favored Clinton more than exit polls showed Live coverage: Tillerson's hearing for State The rise and possible fall of the ‘Card’ in politics MORE (D-Colo.) of opposing construction of the Keystone XL pipeline.
The conservative grassroots group claims Udall, who is up for reelection this year, wants to kills the $5.4 billion project. The ad is set to run through May 23.
"Sen. Mark Udall is siding with Washington lobbyists and special interests to kill it," the ad states.
The energy alliance says Udall opposes the pipeline because he voted against an amendment in 2012 that would have approved construction, and two other amendments in 2013 that would have promoted investment in refining sectors through the pipeline.
Udall has yet to take a formal stance for or against the pipeline.
Udall spokesman Mike Saccone said the reason the senator didn't vote for the Republican and Democratic budget amendments on Keystone last year was because he felt it wasn't Congress' place to do so.
"Sen. Udall still believes Congress should not be injecting politics into the review process," Saccone said.
Rep. Cory GardnerCory GardnerGraham: Ryan tax plan won’t get 10 votes in the Senate The Hill's 12:30 Report GOP senator argues for Gitmo expansion: ‘It ain’t Martha Stewart' being put there MORE (R-Colo), who is running against Udall, backs Keystone's construction and has worked to turn the pipeline into an issue in the race.