The U.S. government could be hiding sensitive information from the public about a major trans-border pipeline proposal, a lawsuit filed Wednesday alleges.

Three green advocacy groups are suing State Secretary Hillary Clinton, demanding she release any communications between herself and Paul Elliott, an oil industry lobbyist.

Elliott is being paid $150,000 to lobby on behalf of Calgary-based pipeline heavyweight TransCanada.

His job is to convince Capitol Hill policymakers that it’s in America’s best interest to approve Keystone XL, a proposed 3,200 km pipeline linking Alberta’s oil sands to Gulf Coast refineries.

Friends of the Earth, Corporate Ethics International and the Center for International Environmental Law worry Elliott is wielding “inappropriate influence” in Washington, DC.

The TransCanada lobbyist helped lead Hillary Clinton’s failed campaign for president several years ago. She is now in charge of deciding whether to approve Keystone XL, a decision expected later this year.

The three advocacy groups filed a freedom of information request last December, seeking more information about the relationship between Clinton and Elliott. That request failed.

The groups are now suing Clinton, arguing their request was turned down without sufficient legal merit.

“Why is the State Department refusing to release these communications?” Erich Pica, president of Friends of the Earth, said in a press release.

Wednesday’s lawsuit is the latest environmental offensive in a protracted campaign to block Keystone XL.

Green advocates fear a major oil spill in the American heartland. Their campaign is also widely seen as a proxy battle in the larger war against further development of Alberta’s oil sands.

Reporting from Washington last February, the Tyee asked Jane Moffat, head of the Canadian-American Business Council, for her views on the freedom of information controversy.

“[Friends of the Earth] have raised no new arguments, they’ve raised nothing,” she said at the time. “They just scream on the paper about a bunch of stuff that isn’t even true. I don’t think anybody takes them seriously.”

Geoff Dembicki reports for the Tyee.