In the largest rollback of federal land protection in U.S. history , President Donald Trump significantly reduced the size of two national monuments, opening them up to development and more local control.

The president has decided to reduce Bears Ears National Monument, declared by President Barack Obama in December 2016 , in one of his last moves as president, by nearly 85 percent , according to NPR, as well as reducing Grand Staircase-Escalante National Monument, a monument created by President Bill Clinton in 1996, by nearly 50 percent.

The motion is being called a win for Republican lawmakers and fossil fuel companies , while environmentalists and some native nations argue that the reduction will threaten national heritage and hundreds of thousands of archaeologically significant sites. The northern and southeastern areas of Bears Ears National Monument are home to oil and gas fields , and some of that land will now be free for extraction, National Geographic reported.

The monuments, which were protected under the Antiquities Act, have been viewed as an act of federal overreach depriving Utah residents of their land.

"These abuses of the Antiquties Act give enormous power to the faraway bureaucrats at the expense of the people who actually live here, work here, and make this place their home," Trump said in his visit to Utah Monday , slamming past Democratic administrations.

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Tribal leaders and environmental activists are likely to sue for the decision. In a written statement, the Navajo Nation vowed to defend Bears Ears in court. The statement claims that the Navajo Nation has made repeated requests to speak with President Trump about the monument.

"The decision to reduce the size of the Monument is being made with no tribal consultation," the statement, which was released by the Navajo Nation President Russell Begaye , reads.

Bears Ears, home to ancient artifacts, dinosaur fossils, cave drawings, cliff dwellings and sacred burial grounds, is considered one of the most culturally significant areas in the American Southwest.

"Bears Ears National Monument is not for Native Americans but for all Americans," Vice President Jonathan Nez said. "This is a sad day for indigenous people and for America. However, we are resilient and refuse to allow President Trump’s unlawful decision to discourage us. We will continue to fight in honor of our ancestral warriors who fought for our way of life, for our culture and for our land too.”

Ten conservation groups had filed a lawsuit by late Monday , calling Trump's decision "unlawful." However, President Trump is not the first president to reduce a national monument. President Woodrow Wilson reduced Mount Olympus by 50 percent , and Franklin D. Roosevelt diminished the Grand Canyon Monument by more than 70,000 miles while in office.

The question remains whether the Antiquities Act allows for reduction of national monuments as well as their creation. NPR reported that modifying public lands is historically up to Congress .