The tribal government of the Navajo Nation is preparing to sue President Trump to reverse his decision to significantly shrink Utah’s Bears Ears National Monument.

The Navajos, who consider much of the original 1.4 million-acre monument area to be sacred and culturally significant, plan to file a federal lawsuit with four other nearby tribes who had been pushing for the land protections for decades before then-President Barack Obama Barack Hussein ObamaTwitter investigating automated image previews over apparent algorithmic bias Donald Trump delivers promise for less interventions in foreign policy Rush Limbaugh encourages Senate to skip hearings for Trump's SCOTUS nominee MORE created it last year.

“The Navajo Nation has made repeated requests to meet with President Trump on this issue. The Bears Ears Monument is of critical importance, not only to the Navajo Nation but to many tribes in the region,” Navajo President Russell Begaye said in a Monday statement shortly after Trump signed proclamations reducing Bears Ears and the Grand Staircase-Escalante National Monument, also in southern Utah.

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“The decision to reduce the size of the monument is being made with no tribal consultation. The Navajo Nation will defend Bears Ears,” he continued. “The reduction in the size of the monument leaves us no choice but to litigate this decision.”

The five tribes came together last year to form the Bears Ears Inter-Tribal Coalition to push for the monument’s creation and act as a voice to advise the federal government in management of it. The four other tribes are the Hopi, Ute Mountain Ute, Pueblo of Zuni and Ute Indian Tribe.

Numerous other entities are likely to join the tribes in suing, either on their own or by taking part in the tribal lawsuit.

Outdoor retailer Patagonia has also promised to sue, as have numerous environmental groups.

Opponents of Trump’s reductions are likely to argue that Congress never authorized presidents to eliminate or reduce national monuments. The Antiquities Act allows monuments to be created, but did not explicitly authorize withdrawals.

The Pacific Legal Foundation and other conservative groups have argued that the authority to reverse a previous president’s designations is implicit in the Antiquities Act.

Previous presidents have reduced national monuments, but no one has sued, so courts have not weighed in on the issue.

Not all Navajo Nation members supported Obama’s designation of Bears Ears.

“When Bears Ears was designated, it was disheartening for my community,” Rebecca Benally, a Navajo and a commissioner in Utah’s San Juan County, where the monument is, said before Trump’s speech in Salt Lake City.

“It was insulting that bureaucrats thousands of miles away didn’t believe we were capable of protecting our land,” she said.