Interior Secretary Ryan Zinke is recommending changes to a “handful” of national monuments, according to the Associated Press. Zinke didn’t specify which, but based on an interim report released in June, he may recommend that Bears Ears National Monument in Utah be shrunk in size. If President Donald Trump decides to act on Zinke’s recommendations, that will almost surely lead to litigation.

Zinke’s report to the president comes about four months after Trump signed an executive order directing the Interior Department to review the designation of 27 national monuments created since 1996, and comprising about 553 million acres of land and sea. Trump said the goal of the review was to end an abuse of power that’s resulted in a “massive federal land grab.” But environmental groups and tribal leaders fear that lifting designations would put at risk historical sites and halt safeguards for public lands and waters. It’s unclear whether the areas that could lose federal protection would be open to mining, logging, and oil and gas development — but that’s what environmental groups fear.

Through the years, US presidents of both parties have used the Antiquities Act of 1906 to set aside swaths of public land to protect important historical, cultural, and ecological sites without approval from Congress. The designation allows authorities to restrict activities such as grazing, farming, logging, and mineral mining. But protections vary from place to place. Generally, existing oil and gas development can continue, says Dan Hartinger, the national monuments campaign manager at the Wilderness Society.

President Barack Obama used the Antiquities Act to protect more land and water than any other US president. In his final days in office, he created the controversial Bears Ears National Monument, which protects 1.35 million acres of land in southeastern Utah. The designation was seen as an overstep of presidential authority by many Republicans and some local residents, but it was hailed by Native Americans who consider the area sacred and wants to protect archaeological and burial sites from vandalism.

No president has ever eliminated a monument altogether, but some have trimmed boundaries almost 20 times. Woodrow Wilson, for instance, sliced Mount Olympus National Monument nearly in half, which Theodore Roosevelt had created. The last president to reduce the size of a monument was John F. Kennedy who, in 1963, revised the boundaries of the Bandelier National Monument in New Mexico.

Zinke sent his report to the While House, the Interior Department said, but he did not make it public. In an interview with the Associated Press, Zinke said he did not recommend eliminating any national monuments. Alongside Bears Ears, another monument that’s seen at risk of losing federal protections is the Grand Staircase-Escalante National Monument, in Utah. It was created by President Bill Clinton in 1996, sparking an outcry at the time, in part because it cut off valuable coal reserves in the area from mining. Before the release of the final report, Zinke had already announced that six national monuments, including Grand Canyon-Parashant in Arizona and Canyons of the Ancients in Colorado, would stay unchanged.

If Trump decides to go through with Zinke’s recommendations and shrink the size of national monuments, there’s likely going to be litigation. “This is very likely to become a legal issue,” says Hartinger. “We will almost surely see a flurry of litigation filed from a number of groups.” That include environmental groups like the Wilderness Society, tribal leaders, and state attorney generals, he says. And because there’s no precedent, it’s unclear what will happen.

What’s sure, according to Hartinger, is that there’s going to be public backlash. During a two-month period of public comments, the Interior Department received more than 2.4 million comments — and an overwhelming majority was in favor of keeping the national monuments, according to the Center for Western Priorities. Most Americans support protecting public lands, parks, and historical places, Hartinger says — and many of them are traditionally conservative constituents like hunters and fishermen. 

“Whether it’s bighorn sheep hunters in Arizona, business owners in Utah, or tribal leaders in the Navajo Nation,” Hartinger says, “this is something that cuts across partisan and political lines and has a very real impact on people.”

Update August 24th, 4:25PM ET: The story was updated to indicate that the final report was sent to the White House but not released publicly.