U.S. senators who drafted legislation in support of the Keystone XL oil pipeline received $21 million from the oil industry, an advocacy group says.

U.S. Sens. John Hoeven, R-N.D., and Mary Landrieu, D-La., chairwoman of the Senate Energy Committee, introduced legislation that would immediately authorize pipeline company TransCanada's application to build Keystone XL.

Oil Change International, an advocacy group opposed to Keystone XL, said Hoeven and Landrieu received campaign support from the oil industry. It said Thursday its review of campaign contributions finds the nine Democratic senators who joined the entire rank of Senate Republicans in co-sponsoring the bill received an average $375,000 each in "dirty energy money."

TransCanada submitted an application to the U.S. federal government to build the pipeline across the U.S.-Canadian border. A decision on the application is pending because of legal issues over the pipeline's route through Nebraska.

Landrieu said five federal studies on the impact of the pipeline have been completed since TransCanada submitted its application more than five years ago. The government needs to review the environmental drawbacks of the pipeline to determine its national interest.

"This pipeline is clearly in our national interest, and I urge all senators to join Sen. Hoeven and me to support this bill," she said in a statement.