President Trump is preparing an executive order targeting a massive national monument in Utah, a key part of former President Obama's conservation legacy.

Obama created the 1.3 million-acre Bears Ears National Monument in late December using his unilateral power under the Antiquities Act.

The action drew heavy backlash, with conservatives accusing him of shutting down development of fossil fuels or other land uses without concern for local economies.

Trump is expected to sign an order Wednesday to examine all national monuments going back two decades, a White House official said.

But people familiar with the order say it's directed primarily at Bears Ears and at Utah's Grand Staircase-Escalante National Monument, which former President Clinton created in 1996. That monument also faced loud opposition due in part to planned mining in the area that was shut down.

Interior Secretary Ryan Zinke will be formally asked to recommend any executive or legislative changes if he finds improper use of the Antiquities Act.

"Past administrations have overused this power and designated large swaths of land well beyond the areas in need of protection," the official said, saying that the law is meant for areas of "historic or scientific value."

But Trump's options after the order are limited. Conservationists and experts say the Antiquities Act doesn't give Trump the power to rescind monuments or greatly reduce their size.

Nonetheless, opponents of Bears Ears are cheering Trump's order. Utah's statewide leaders are united in their opposition to the monument, and the legislature has passed a resolution asking that Trump to take some sort of action.

"Anyone who has read the actual text of the Antiquities Act knows that the law has been greatly abused by recent administrations. I commend President Trump for instigating a review of past designations," Sen. Mike Lee (R-Utah) said in a statement.

"I do think it is a worthwhile endeavor to look at the abuse of the Antiquities Act," said Kathleen Sgamma, president of the Western Energy Alliance, which represents oil and gas companies.

"It was originally designed to protect specific cultural resources that were under imminent threat of being raided or destroyed," she said. "Obviously, they've gone well beyond protecting specific cultural resources and they are being used to just lock away land with broad strokes, with no consideration of what's going on on the ground."

Trump's action will also mark a new chapter in the fight over federal land in the West, which has raged for decades and reached new heights under Obama.

"There are some very vocal, very upset people that have sincerely felt pain," said John Ruple, a professor at the University of Utah's law school who studies public land.

Opponents of monuments, he said, "feel like they have an opportunity here with a new administration in place and with Republicans in control of both houses of Congress, so they're taking advantage of that."

Bears Ears, named for a pair of mesas, was created mostly to protect areas sacred to numerous American Indian tribes whose ancestors lived there. The area contains numerous historic and natural resources.

Obama used the Antiquities Act to protect more land and water than any president before him, with 26 new or expanded monuments totaling more than 550 million acres.

Most of the large monuments have encountered opposition, including Katahdin Woods and Waters in Maine, the Papahanaumokuakea Marine National Monument off the coast of Hawaii and Organ Mountains-Desert Peaks in New Mexico.

All of those monuments could be targeted under the review Trump is ordering.

But experts and supporters of the national monument law say Trump can't rescind designations because the Antiquities Act doesn't explicitly provide for that.

"Clearly the president has the authority to create it. The question is: Where would he get the power to undo it, or significantly reduce it?" Ruple said. "The Antiquities Act says nothing about undoing monuments or reducing it."

The Center for Western Priorities agrees.

"There's a reason no president has attempted to rescind a monument designation. It's not provided for the Antiquities Act," said Aaron Weiss, spokesman for the conservation group.

"Any review that ignores that is willfully ignoring the law and just setting this administration up for years of lawsuits."

The courts have not weighed in on the issue, so Trump's actions could provide legal precedents.

Many Republicans, including Lee, argue that any power Congress gives to the president can be reversed by a future president.

The Center for Western Priorities has been fighting for months in support of national monuments and predicts that Trump will try to fight Obama's monuments.

The group is running a multi-pronged advertising campaign showcasing monuments, including Bears Ears, in an effort to frame the issue as one about protecting parks and majestic landscapes.

"This is a sustained, ongoing, major attack on America's parks and public lands," Weiss said.

Just over half of Utah voters opposed Bears Ears in a January poll from the Salt Lake Tribune and the University of Utah, and almost as many supported action to overturn the designation. Thirty-four percent supported the monument.