A prominent House Republican says he's ready to play hardball to obtain documents about the Keystone XL pipeline from the State Department.

In a new letter to Secretary of State John Kerry, House Oversight and Government Reform Committee Chairman Jason Chaffetz says State hasn't complied with a February request for copies of other departments' input on TransCanada Corp.'s project, which remains under federal review.

"If the department remains unwilling to work with the committee on a voluntary basis, we are left with no alternative but to consider the use of compulsory process to obtain the materials we requested on February 24, 2015," Chaffetz writes.

Chaffetz wants comments from other departments to State about whether the project is in the "national interest."

The letter arrives amid a larger battle over transparency at the State Department and other agencies. Chaffetz recently held a two-day hearing that aired a suite of grievances about excessive delays and redactions in response to public-records requests.

And the State Department is in the thick of its review of thousands of pages of emails turned over from Hillary Clinton's private email server.

With respect to Keystone, a number of agencies filed comments with State, which were not made public, earlier this year on the project. Keystone XL would bring hundreds of thousands of barrels per day of oil from Alberta's oil sands across the border en route to Gulf Coast refineries.

The 2004 executive order that's governing State's review of the multibillion-dollar proposed pipeline calls for consultation with major departments and agencies, including Justice, Interior, Commerce, Transportation, Energy, Homeland Security, and Environmental Protection Agency.

The letter says State rebuffed the earlier request by claiming they "implicate important executive branch confidentiality interests."

"The committee has proposed several paths forward that would accommodate the department's confidentiality interests while also recognizing the committee's legitimate interest in obtaining the information we requested," the letter states.

Republicans, backed by major business and industry groups, want the Obama administration to permit the project, while Democrats are split on the project that faces bitter opposition from environmentalists.

President Obama is expected to make the final decision and has buoyed Keystone opponents by making several critical comments about the project, but Obama has also left himself political wiggle room.

The State Department did not provide immediate comment on the letter. It is also signed by Rep. Cynthia Lummis, who heads the Subcommittee on the Interior.

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