President Donald Trump just signed an executive order aimed at expanding offshore oil and gas drilling in the Arctic and Atlantic Oceans — and maybe even in the Pacific Ocean. The move, which is expected to lead to litigation in the courts, is the latest attempt to dismantle President Barack Obama’s environmental legacy. Last month, Trump began the process to halt Obama’s cornerstone plan to curb greenhouse gas emissions. And on Wednesday, he signed another executive order that could expand oil and gas development on wilderness areas currently protected as national monuments.

Today’s executive order instructs the Department of the Interior to review locations for offshore oil and gas exploration and leasing that were put off limits by the Obama administration. That includes millions of acres in the Atlantic and Arctic Oceans that Obama withdrew permanently from drilling in December 2016. The order also asks for a review of marine monuments and sanctuaries created in the past 10 years, and prohibits the creation of new ones, according to Interior Secretary Ryan Zinke, who spoke to reporters about the order last night.

The order is expected to lead to litigation in the courts

“This executive order starts the process of opening offshore areas to job-creating energy exploration,” Trump said today before signing the order. “It reverses the previous administration’s Arctic leasing ban ... and directs Secretary Zinke to allow responsible development of offshore areas that will bring revenue to our treasury and jobs to our workers.”

The Interior Department oversees some 1.7 billion acres on the outer continental shelf, the submerged lands off the coasts of the US. The department is responsible for coming up with five-year plans to indicate which offshore locations can be leased for oil and gas development. The latest plan for the years 2017–2022 was finalized under the Obama administration; in a major blow to the oil industry, the plan put certain areas in the Atlantic and Arctic Oceans off limits for drilling, instead allowing leasing in the Gulf of Mexico and in Alaska's Cook Inlet.

Trump is now asking the Interior Department for a review of this five-year plan. As the president, he has every right to. “That is well within the boundary of the Interior Department’s authority,” says Kevin Book, the managing director of ClearView Energy Partners. “It’s the first thing that Obama administration did on offshore drilling when they came into power in 2009.”

Revising the plan, however, will take time, Book tells The Verge. But eventually, the new plan could include offshore areas that were previously put off limits — including waters off the Pacific Coast. Under Obama, those waters were not included in the five-year plan, as the governors of Washington, Oregon, and California voiced opposition to drilling off their shores. But Zinke said that nothing is off the table, according to Bloomberg. “We’re going to look at everything,” Zinke said when asked about potential oil leases in the Pacific Ocean. “A new administration should look at the policies and make sure the policies are appropriate.”

That’s going to be “incredibly unpopular,” says Nancy Pyne, a campaign director at Oceana, an ocean conservation organization that opposes drilling. Pyne says that the president has to consult with the governors of Western states before allowing drilling in Pacific waters. But, eventually, the administration doesn’t have to take their opinions into consideration when making a final decision. “Given this president’s track record of bucking the trend, we’re very worried that he’s going to move forward with drilling off the Pacific Coast as well,” she tells The Verge.

If the Interior Department decides to allow drilling in certain off-limit areas in the Atlantic and the Arctic, that could eventually lead to legal challenges. That’s because Obama indefinitely banned some of the areas from drilling under a 1953 law called the Outer Continental Shelf Lands Act. In December alone, Obama used the law to safeguard 3.8 million acres of the Atlantic Ocean — from southern Virginia to off of Cape Cod — and 115 million acres in the Arctic Ocean — including all of the Chukchi Sea off the northwest coast of Alaska, and most of the Beaufort Sea off Alaska’s northern edge.

It’s unclear whether a new president has the authority to reverse those bans without Congress, says Robin Craig, an environmental law professor at the University of Utah. If, following this executive order, the Trump administration decides to go ahead and open up those areas, environmental groups will likely sue. But because there’s no precedent, it’s unclear what the outcome of those lawsuits will be. “Who knows whether they’ll win or lose,” Book says. “It hasn’t been litigated yet.”

“We’ve fought this before and we’ll fight it again.”

But groups like Oceana are ready to fight. Drilling in Arctic waters is dangerous and there’s no proven way to clean sea ice from potential oil spills, Pyne says. “It’s dark, it’s cold, it’s stormy, and it’s covered in sea ice,” she says. And drilling off the Atlantic and Pacific Coasts is unpopular with businesses and residents in coastal states. Oil spill can negatively affect fishing and tourism, and states just don’t want to risk it. “Regardless who’s in the White House coastal communities and businesses do not want offshore drilling off their coast,” Pyne says.

So today’s executive order is probably the beginning of a long fight in the courts. “We’ve fought this before and we’ll fight it again,” Pyne says.