Rep. Fred Upton, R-Mich., chairman of the House Energy and Commerce Committee, and House Investigations Subcommittee Chairman Tim Murphy, R-Pa., sent a letter to Environmental Protection Agency Administrator Gina McCarthy asking about any ties with the Sierra Club.
House leaders point to a report from Fox News saying a Freedom of Information Act request indicates the EPA may have discussed Sierra Club's "anti-Keystone agenda" off the record.
Upton and Murphy said Wednesday that communication with parties outside the EPA is encouraged, but "we want to be sure those officials do not inappropriately share non-public planning and deliberative documents in a manner that undermines trust in the agency's process."
Keystone XL, a cross-border oil pipeline from Canada, needs federal approval. The pipeline is controversial in part because the more viscous type of crude oil from Canada is seen as an environmental threat.
President Obama said he'd weigh the national interest of the pipeline against its environmental footprint.
Upton has been one of the more vocal supporters of the pipeline. He asked McCarthy to reply by Feb. 21.
Notable deaths of 2014 [PHOTOS]
EIA: Russia diversifying energy production