The Interior Department plans to remove or cover up all “inappropriate content” at national parks and sites by Sept. 17 and is asking the park visitors to report any “negative” information about past or living Americans, according to internal documents.

It’s a move that historians worry could lead to the erasure of history involving gay and transgender figures, civil rights struggles and other subjects deemed improper by the Trump administration.

Staff at the National Park Service, which is part of the Interior Department, were instructed to post QR codes and signs at all 433 national parks, monuments and historic sites by Friday asking visitors to flag anything they think should be changed, from a plaque to a park ranger’s tour to a film at a visitor’s center.

Leaders at the park service would then review concerns about anything that “inappropriately disparages Americans past or living (including persons living in colonial times),” according to slides presented this week at a meeting with park superintendents. By Sept. 17, “all inappropriate content” would be removed or covered, according to the presentation.

The signs already are up at many national parks, including sites that commemorate difficult periods in American history like the Minidoka National Historic Site in Idaho, where more than 13,000 Japanese Americans were incarcerated after being forcibly removed from their homes without due process during World War II.

“Our history isn’t always perfect,” said Theresa Pierno, the president of the National Parks Conservation Association, a nonprofit group that supports national parks and opposes the planned changes. “How do you talk about Martin Luther King without talking about racism?”