In an unprecedented and arguably illegal move, President Donald J. Trump has announced that he will substantially reduce the boundaries of two national monuments in the state of Utah.

At a rally in Salt Lake City yesterday afternoon, Trump told a crowd of supporters that he will shrink Bears Ears National Monument, a parcel of public land with major recreational and archeological significance that has become a rallying cry in the outdoor industry’s battle to protect public lands, by 1.1 million acres, a total 85 percent.

Courtesy of the Wilderness Society

He also announced plans to whittle away some 800,000 acres of the Grad Staircase-Escalante National Monument, which amounts to about 46 percent of the monument’s overall acreage.

Not only is this move the largest reduction of public land protection in United States history, but it is the first time that a sitting president has attempted to modify any existing national monument in more than half a century.

The national monument classification system was brought about in June of 1906 when President Theodore Roosevelt signed the Antiquities Act into law. The act gives the President of the United States authority to protect swaths of federal land with significant natural, cultural, or scientific features.

One major catalyst for the Antiquities Act was the continued looting and desecration of important architectural sites in the Southwest such as Chaco Canyon and Cliff Palace.

Many national monuments, including the Grand Canyon, Grand Teton, Bryce and Zion just to name a few, have gone on to become national parks.

But Donald Trump views the protection of Bears Ears and Grand Staircase-Escalante as an overreach of federal authority, and he used his Salt Lake City rally as a way to pander to supporters who share his belief.

“I don’t think it’s controversial, actually, I think it’s so sensible,” he said in his speech.

He went on to claim that the designation of Bears Ears and Grand Staircase as national monuments had impeded the ability of Native Americans to use the land for long-held, sacred traditions.

In reality, the local tribes comprise some of the loudest voices calling for the continued protection of Bears Ears. In fact, the Bears Ears Inter-Tribal Coalition, made up of five area tribes, now plans to sue Trump for what they perceive as an illegal usurpation of federal power, and they’re not alone in their resistance.

Reaction from the outdoor industry has also been swift. Patagonia—one of the first companies to withdraw from the formerly Salt Lake-based Outdoor Retailer trade show before plans were announced to relocate the event to the more public land-friendly state of Colorado—is sporting a bold statement on it’s website, informing patrons of what it perceives as an outright act of theft by the Trump Administration.

Environmental and conservation groups have condemned the move across the board. According to Wilderness Society, which will also be filing suit, “the reductions (of Bears Ears and Grand Staircase) are widely assumed to be a way to open more of these priceless landscapes to mining and drilling.”

Backcountry Hunters and Anglers CEO Land Tawney, called yesterday a ” dark day” for the nation’s hard-earned conservation legacy.

“America’s conservation legacy defines us and is the envy of the world,” he said. “Today is a dark day for that legacy. Roosevelt is shaking his fists! Undermining one of our bedrock conservation laws and selling out to industry flies in the face of T.R. (Theodore Roosevelt), who President Trump said he wanted to emulate.”

The Sierra Club also came out strong against Trump’s controversial announcement.

“Today’s announcement is a disgrace,” Sierra Club executive director Michael Brune said. “It’s an insult to tribal sovereignty, centuries of Latino heritage, and to people across the country who love and care about our great outdoors. Yet again the Trump administration has sold out the American people and our special places—all to benefit the fossil fuel elite.”

Ensuing law suits will inevitably argue that Trump lacks the authority under the Antiquities Act and the United States Constitution to rescind previously designated national monuments. But some environmentalists worry that if Trump wins his court battles, it could set a troubling precedent of using the presidency to transfer federal lands to the states.