SALT LAKE CITY — Although there's been no formal announcement from the White House on what may happen to monument boundaries based on recommendations from Interior Secretary Ryan Zinke, a coalition of conservation groups Thursday said it's readying a lawsuit.

If the boundaries of monuments in Utah, New Mexico, Nevada or elsewhere are reduced, opponents vow that a legal war is on.

"The Conservation Lands Foundation and its partners are prepared to make every effort possible to ensure that our national monuments remain as they are," said Bryan Sybert, the foundation's executive director. "We are prepared to pursue that protection and defense in the courts if necessary."

Sybert moderated a teleconference hosted by the foundation on the looming announcement by the White House and the fear that monuments, particularly in Utah, will see significant boundary reductions.

One number that has been attributed to unnamed congressional aides by multiple media outlets is 160,000 acres — the possible new size proposed for the 1.35 million-acre Bears Ears National Monument designated late last year by former President Barack Obama.

The Conservation Lands Foundation, joined by Utah Dine Bikeyah, Friends of Cedar Mesa, Archaeology Southwest, Patagonia Works, the Access Fund and National Trust for Historic Preservation, have retained the services of Doug Wheeler, a partner with Hogan Lovells, a multinational law firm with headquarters in London and Washington, D.C.

"Monuments that are modified substantially need to be protected as a matter of law," Wheeler said, noting that the Antiquities Act does not give a U.S. president the authority to significantly alter boundaries designated by a predecessor.

Wheeler said past presidents have made boundary adjustments out of necessity, but the Antiquities Act makes clear that signficant changes are in the purview of Congress, not the U.S. president.

Monument critics, however, argue otherwise, and no monument boundary modification has been tested in court.

In 1938, President Franklin D. Roosevelt asked the U.S. attorney general whether he had the power to abolish a national monument. Homer Cummings said no, but critics of that "cursory" opinion say it was flawed and never adopted by any court.

Proponents of downsizing Utah's national monuments argue that the monument review zeroed in on places like Bears Ears and Grand Staircase-Escalante because of their size. Together, they exceed 5,000 square miles.

Language in the Antiquities Act says presidents should make designations that are "compatible with the smallest" area to protect the at-risk antiquities.

Gavin Noyes, executive director of Utah Dine Bikeyah, said the probable reductions in the size of monuments is contrary to what the American public wants based on the millions of comments received during a public comment period.

The organization is continuing to make its voice heard over the monument's fate, Noyes said.

Zinke's list of recommendations were given to the White House on Aug. 24 after an executive order from President Donald Trump directed a review of 27 national monument designations of 100,000 acres or more.

The monuments under review are bookended by Utah's Grand Staircase-Escalante, designated in 1996, and Bears Ears, created last year.