WASHINGTON (AP) — A House panel has issued a subpoena to Secretary of State John Kerry for department documents, reports and letters related to the contentious push to build the Keystone XL pipeline.

Republicans on the House Oversight and Government Reform Committee announced the subpoena on Wednesday.

The $8 billion pipeline would transport oil harvested from Canada’s tar sands to pipelines linked to refineries on the Gulf of Mexico and in western Illinois.

Earlier this year, Congress approved legislation to build the pipeline and sent the measure to President Barack Obama. The president vetoed the bill and the GOP-run Senate failed to override the veto in March.

President Obama has said that the bill circumvented the well-established process for approving cross-border pipelines, which must be determined to be in the national interest.