Trump has, in the past, said reducing the size of the monuments designated by former Presidents Bill Clinton and Barack Obama would represent an end to “another egregious abuse of federal power” and, at the same time, “give [power] back to the states and to the people where it belongs.”

Here’s what you need to know about the changes, which—according to the AP—mark the first time in 50 years that a president has tried to roll back these kinds of land protections:

The cuts

Monday’s announcement in Salt Lake City is expected to reduce the size of two national monuments: Bears Ears, currently 1.3 million acres of land in southeast Utah, will shrink by 85%, while Grand Staircase-Escalante, 1.8 million acres of land in southern Utah, will get chopped by nearly 50%. Bears Ears was created near the end of President Obama’s second term in office based on its cultural and historical importance. It features tens of thousands of archeological sites, including ancient cliff dwellings. Grand Staircase-Escalante, meanwhile, was designated as a monument by President Clinton because of its “un-spent wealth of ancient and modern science and culture.“

The Washington Post—Getty Images

A long time coming

President Trump’s Monday afternoon address caps a months-long process by the administration to reduce the plots of land. In April, Trump asked Zinke to review more than two dozen national monuments because he said their designation was an example of government overreach under previous administrations. Utah’s Republican congressional delegation had pushed the Trump administration to take action on the lands, with Senator Orrin Hatch (R-UT) playing an especially instrumental part. The delegation argued the monuments locked up too much land from commercial use and development.

Progressive groups are against the move. They argue the cultural, historical, and scientific value of the land warrant protection.

George Frey—Getty Images

Tribes plan to sue

In fact, five Native American tribes and conservation groups plan to sue the administration to stop any changes based on separation of powers and the Antiquities Act of 1906. Among those planning the legal action is the Bears Ears Inter-Tribal Coalition—made up of the Hopi, Navajo Nation, Ute Mountain Ute Tribe, Pueblo of Zuni, and the Ute Indian Tribe—which was the group that originally advocated for the monument. Several Native American tribes consider the land sacred; the sites contain “tens of thousands of archaeological sites.”

Other monuments on the chopping block

Eight other national monuments may meet the same fate as Bears Ears and Grand Staircase-Escalante. Zinke’s review of 27 sites recommended shrinking or lifting restrictions on ten in total. That could mean the government will start allowing commercial fishing or logging on some other public lands.