A coalition of Native American tribes said it will sue the Trump administration by the end of the day for President Trump's decision to shrink the Bears Ears National Monument in Utah.

“What the president has purported to do is outside the scope of his authority,” said Navajo Nation Attorney General Ethel Branch on Monday. "We think the law is clear."

"We are filing a joint complaint by the five nations,” Branch added, according to a tweet shared by the Bears Ears Inter-Tribal Coalition. “We anticipate filing by the end of the day."

President Trump on Monday announced during a visit to Utah’s capitol that he will shrink Utah’s Bears Ears and Grand Staircase-Escalante national monuments, framing the decision as a sharp rebuke of former President Barack Obama's use of executive authority to set aside public land for protection.

The Trump administration and congressional Republicans say previous presidents abused their authority under the 1906 Antiquities Act to unilaterally declare national monuments, setting aside larger and larger swaths of public land, limiting development opportunities and stifling local control.

The Antiquities Act specifies that national monuments should cover "the smallest area compatible with proper care and management of the objects.”

But supporters of the monuments note the Antiquities Act does not explicitly give authority to presidents to reduce the size of national monuments, although some have done so on a limited scale. The concept has not been tested in court.

Trump is reducing the 1.35 million acres of Bears Ears, established by Obama, to 201,876 acres, and Grand Staircase, created by former President Bill Clinton in 1996, from 1.7 million acres to 1 million.

Under Trump’s proposal, Bears Ears would be divided into two smaller monuments: Indian Creek National Monument and the Shash Jaa National Monument.

Grand Staircase-Escalante would be split into three areas: Grand Staircase National Monument, Kaiparowits National Monument, and Escalante Canyons National Monument.

The Bears Ears Inter-Tribal coalition urged Obama to designate Bears Ears as a monument. The coalition consists of Navajo, Hopi, Uintah and Ouray Ute, Ute Mountain Ute, and Zuni.

Obama created Bears Ears just before he left office, protecting a vast area of mesas and canyons in Utah's poorest county. It is an area in the southeastern part of the state that the tribes consider sacred and depend on for sustenance and cultural tradition. It has more than 100,000 Native American archeological and cultural sites, according to the coalition.