"We are prepared to challenge immediately whatever official action is taken to modify the monument or restructure any aspect of that, such as the Bears Ears Commission," Ethel Branch, Navajo Nation attorney general, told Reuters.
The tribe believes that the reduction of Bears Ears' boundaries violates the Antiquities Act, a 1906 law designed to protect archeological sites from looting and vandalism and allows presidents to designate the lands as national monuments without going through Congress.
In December, President Obama used his authority under the Antiquities Act to designate 1.35 million acres of land as the Bears Ears National Monument, which contains 100,000 significant Native American sites.
In Zinke's leaked memo to President Trump, the secretary advised changes to at least 10 national monuments, including shrinking Bears Ears.
According to records obtained by the Salt Lake Tribune, Utah lawmakers have submitted maps and documents to the Interior Department to drastically reduce Bears Ears' size by 90 percent, or down to only 120,000 acres.
As Climate Nexus reported, while the land in Bears Ears is not thought to contain significant oil or gas deposits, mining and fossil fuel interests cheered Zinke's recommendation as a preview of how the Trump administration may handle scaling back protections for more oil and gas-rich federally protected land.