The Obama administration concealed American Indians’ appeals to reject the Keystone XL pipeline, according to a report published Tuesday by The Hill.

The nations had written to the Department of the Interior, claiming the TransCanada tar-sands vessel would jeopardize the cleanliness of resources, infringe upon prior treaty agreements, and violate sacred lands, in stacks of letters only revealed through Freedom of Information Act Request.

“Interior sent 175 pages of letters from tribes to the State Department, according to documents obtained by The Hill,” the daily reported. “But the most crucial document sent by the department—Interior’s own view of Keystone—remains secret.”

The publication noted that the “Obama administration did not publicize the submissions” and that Interior “declined to disclose its comments on Keystone, as well as any correspondence between it and the State Department—the primary focus of The Hill’s FOIA request.”

The Department of the Interior told the paper that the decision to publish its work on Keystone can only be made by the State Department.

Spokesperson Jessica Kershaw also said that Interior has called on State “to give appropriate consideration to comments previously submitted during the Keystone XL permit review process as well as concerns expressed by some tribes in Indian Country about the project.”

Interior, along with seven other agencies, had been tasked with filing comments on Keystone to the State Department, which is currently deciding the fate of the project. The input was due in early February.

The 175 pages of grievances filed by American Indian tribes covered a range of concerns.

The Great Plains Tribal Chairman’s Association, an umbrella organization representing 16 tribes in the Dakotas and Nebraska, told the Obama administration that Keystone would threaten “thousands of sacred and cultural resources that are important to our life-ways and for our future generations.”

The South Dakota-based Oglala Lakota let Interior know that it “continues to fully and completely oppose the approval of the TransCanada Keystone XL pipeline” based on concerns about water pollution.

TransCanada told The Hill that it is aware of indigenous nations’ thoughts on Keystone, but claimed that their safety and environmental concerns are not merited.

The pipeline is not slated to cross any indigenous lands, but experts have said American Indians’ concerns are valid.

Last month, Congress failed to override a Presidential veto of legislation that greenlighted Keystone.

While the move was celebrated by greens, the White House rejection primarily cited concerns about “established executive branch procedures”–although it did say that deliberative process is weighing “security, safety, and environment.”

In February, the Environmental Protection Agency gave the administration an opening to reject the deal when it said the State Department’s Keystone impact assessment failed to account for “improved” analyses, which, it said, are “clear that oil sands crude has significantly higher lifecycle greenhouse gas emissions than other crudes.”

The Hill suggested that widespread tribal opposition to Keystone “could give [Obama] some ammunition to shoot down the project,” but indigenous nations have already made their protests known before in recent months.

In November, the President of the Rosebud Sioux tribe in South Dakota called the Congressional push to have Keystone built “an act of war” in violation of the 1868 Treaty of Fort Laramie.

“I pledge my life to stop these people from harming our children and our grandchildren and our way of life and our culture and our religion here,” Cyril Scott said.