President Donald Trump announced Monday that his administration will roll back federal protections on 2 million acres of land in two national monuments in Utah.

The Bears Ears monument — which was designated by President Barack Obama in one of his last acts in office — stands to lose 1.1 million acres, or 85 percent, of its land area, and the Grand Staircase-Escalante monument will be reduced by 800,000 acres, or 45 percent. The rollback is the first step to opening up these lands to more development and agriculture. The proposal breaks Bears Ears into two separate monuments and Grand Staircase-Escalante into three.

“Some people think the natural resources of Utah should be controlled by a small handful of very distant bureaucrats located in Washington,” Trump said in Utah’s capital Monday, in a speech announcing the changes. “They’re wrong.” The move, he said, is to “to reverse federal overreach and restore the rights of this land to your citizens.”

But he also nodded toward economic interests, saying that federal oversight has led to “unnecessary restrictions on hunting, ranching, and responsible economic development.”

In attempting to decrease the size of the monuments, Trump is stepping into uncharted legal territory. Five Native American tribes — the Navajo Nation, Hopi, Ute Mountain Ute Tribe, Ute Indian, and Pueblo of Zuni — have joined in a lawsuit against the Trump administration, charging that the president of the United States has no power to decrease the size of national monuments like Bears Ears.

Trump, in his announcement about the changes, claimed they would benefit Native Americans. “We’ve seen how this tragic [federal] overreach has prevented many Native Americans from having a voice on their sacred lands, where they practice their most important ancestral and religious traditions,” Trump said. Never mind the fact that the tribes were the ones that had, for years, been asking the Obama administration for the monument protections.

A separate lawsuit — filed by 10 environmental groups, including EarthJustice, the Wilderness Society, and the Natural Resources Defense Council — makes a similar argument, but for the Grand Staircase-Escalante monument.

The result of these lawsuits will set precedent. And as it stands, there’s never been a ruling on whether a president can decrease the size of a national monument. “If this unprecedented and unlawful action is allowed to stand, the 129 national monuments across the United States will be at risk,” the Native American tribes write in their lawsuit.

The Antiquities Act, explained

The Antiquities Act of 1906 gives the president of the United States broad power to set aside special and historically significant publicly owned land for protection as a national monument. These places tend not to have the tourism infrastructure (and gift shops) of national parks, but they are similarly protected from development, and are often beacons for tourists and adventure travelers.

In the past, presidents have shrunk or altered the size of national monuments. President Woodrow Wilson, for instance, cut the size of Mount Olympus National Monument (in Washington state) in half to provide timber for World War I, and Franklin Roosevelt shrank the Grand Canyon when it was a national monument. These moves were not challenged in court, the New York Times reports.

But Trump’s move is much more dramatic. It represents “the most significant reductions by any president,” as the Washington Post explains. The reductions are larger than the state of Delaware.

The Antiquities Act gives the president broad, unilateral power to preserve “historic landmarks, historic and prehistoric structures, and other objects of historic or scientific interest” that are on lands owned by the federal government. But it makes no mention of decreasing the size of these monuments or removing them altogether.

Which means it’s not clear if Trump’s move will hold legal muster. And environmental groups and the Native American tribes that pushed for the creation of these monuments have vowed to fight it tooth and nail.

We can expect a particularly fierce fight for Bears Ears, which has spiritual and historical significance for five Native American tribes in Utah. The park is named for the twin buttes (tabletop hills) that stick out above the desert surrounding them in the southeast part of the state. It is home to thousands of archaeological sites, ancient dwellings, ancestral hunting grounds, and burial grounds.

President Obama declared Bears Ears a national monument as one of his final acts as president. The designation gave governing authority over the land, in part, to the tribes. Critics of Obama’s move said the 1.3 million acres set aside for this monument is a far larger area than needed to protect the tribal history of the area. But Trump’s decision today to decrease the monument is bound to feel like an insult to Native Americans’ history.

Grand Staircase-Escalante, the other monument slated to be downsized, is the largest national monument in the country. The monument has been a treasure trove for dinosaur fossils — and some 21 dinosaur species have been discovered there.

When it was designated as a monument by President Bill Clinton in 1996, cattle grazing was prohibited on the land. Rolling back the national monument designations would open up the possibility for increased livestock grazing, and natural resource prospecting, on these lands.

Prepare to see this go to court

The backlash against Trump’s announcement was swift. “The president stole your land,” the homepage of the outdoor retailer Patagonia, which has been lobbying hard in favor of public lands, now reads. “The decision also undermines the integrity of the Antiquities Act,” REI wrote in response.

Protests also erupted in front of the Utah Capitol.

As disappointing as Monday’s decision was for tribal leaders and conservation groups, they have been preparing for a legal battle over the monuments with the Trump administration for months. For one, Trump in April called Obama’s record of creating national monuments an “egregious abuse of executive power.” And he and Interior Secretary Ryan Zinke have been seemingly hell-bent on reversing as many Obama-era policies as possible.

In April, Trump issued an executive order directing Zinke to review 27 national monuments designated over the past 20 years. In August, Zinke released a report that concluded that none of the monuments warrant complete removal, but “recommended shrinking some of the monuments as well as changing what activities are allowed on the federal lands,” as Vox reported at the time.

The result of the expected legal challenges will have far-reaching consequences. They’ll clarify the degree to which a president can undo conservation efforts. “If courts [uphold] the president’s changes, the door would be wide open for future presidents to regularly reverse their predecessors’ national monument decisions,” University of Utah law professor Robert Keiter explains in the Conversation.

National monument designations are meant to ensure consistent protection for public lands. If courts favor Trump, then those protections could become fleeting.

Over his eight years in office, Obama designated more monuments — for a total of 553 million acres — than any of his predecessors.