The ad, which was scheduled to first broadcast Sunday, is part of the Californian's political action committee's attempt to halt the pipeline, which would carry crude oil 1,700 miles from the oil sands in Alberta, Canada, to refineries in the Gulf Coast, The New York Times reported Sunday.
Because the pipeline would cross the border from Canada to the United States, it needs approval from the U.S. State Department.
"Mr. President, you've had real accomplishments when it comes to fighting climate disruption," Steyer says in the ad. "Let's do the right thing on Keystone."
Opponents of the pipeline are concerned it would contribute significantly to carbon pollution. Proponents boast about the number of jobs the project would create.
"The truth? Scientists report Keystone oil would produce as much carbon pollution as 620,000 cars every year," Steyer says in the ad.