The Navajo Nation and four other American Indian tribes said Tuesday they had sued President Trump to undo his action reducing the Bears Ears National Monument in southern Utah.

The federal lawsuit, which the tribes had long promised, argues that Trump did not have the legal authority to remove more than 80 percent of the land protections that former President Barack Obama Barack Hussein ObamaMichelle Obama and Jennifer Lopez exchange Ginsburg memories Pence defends Trump's 'obligation' to nominate new Supreme Court justice The militia menace MORE had established in 2016.

“Through the Antiquities Act, Congress delegated to the president the limited authority to designate national monuments and retained to itself the power to revoke or modify national monuments,” the tribes wrote in a statement.

ADVERTISEMENT

“The proclamation signed by President Trump today is so extreme that it revokes and replaces Bears Ears and thereby violates the Antiquities Act and seizes authority that the Constitution vests solely in Congress.”

Even though previous presidents have cut national monuments, supporters of Bears Ears say the Antiquities Act does not specifically address recisions, so Trump’s actions are illegal.

Trumps supporters, such as the Pacific Legal Foundation, disagree. They say that the ability to undo monument designations is implicit in the Antiquities Act, since presidents have the authority to create them.

The Navajo Nation, Hopi Tribe, Zuni Tribe, Ute Indian Tribe and Ute Mountain Ute Indian Tribe consider much of Bears Ears to be religiously and historically valuable, though the land is owned by the federal government.

For years, the tribes had pushed for the federal government to protect the land, joined by environmental groups. When Congress failed to protect it themselves, Obama created the national monument, amid strong opposition from Republicans and local Utah leaders.

In addition to reducing Bears Ears, Trump on Monday cut about half of the acreage of the Grand Staircase-Escalante National Monument, also in southern Utah.

A coalition of environmental groups sued late Monday to undo that monument’s reduction.