President Donald Trump signed an order on Feb. 28 directing regulators to review an Obama administration rule that expanded the number of federally protected waterways as the new president targets environmental regulations conservatives label as government overreach.

Trump’s executive order directs the Justice Department to ask a federal court to put legal challenges to the rule on hold as the administration conducts its review, a senior official said.

The order, which the White House did not immediately make public, will kick off what will likely be a lengthy process to undo the Waters of the United States (WOTUS) rule, finalized by the Environmental Protection Agency and the U.S. Army Corps of Engineers in 2015 to clarify which bodies of water are covered by the Clean Water Act.

Trump said during the signing that the Clean Water Act should apply only to navigable waters that affect interstate commerce.

“A few years ago the EPA decided that navigable waters can mean nearly every puddle or every ditch. It was a massive power grab,” Trump said.

The rule has faced intense political and legal opposition from Republican lawmakers, farmers and energy companies. It was blocked by a federal appeals court pending further court challenges.

Federal law requires that the administration undertake a formal evaluation of the rule before a decision is made about whether to rescind the regulation, the senior official said, adding that the review would likely take a “long time to get through.”

The Environmental Protection Agency under former President Barack Obama said the rule protected waters that are next to rivers and lakes and their tributaries “because science shows that they impact downstream waters.”

Dozens of agricultural groups, states and municipalities had sued to block the rule. The challengers contended the EPA’s move had improperly expanded federal regulatory power.

The conservative Heartland Institute issued a statement in support of the president’s action and dismissing claims by opponents.

“No doubt that environmental NGOs will describe this order in hysterical terms, confidently predicting an environmental disaster on the order of Chernobyl, for it is difficult to make a different call when your playbook has but one play,” the organization said in a statement to media. “No doubt the mainstream media wring their hands and shed crocodile tears, without bothering to even attempt to understand—much less accurately explain—the detailed technical and regulatory issues that make this common-sense order such a wise move.

“Those of us in the trenches who deal with EPA excess have, quite literally, hundreds of examples where the EPA and Army Corps made wetlands designations that would appall any reasonable person possessed with an ounce of common sense,” the statement continued. “This was the case before President Obama’s WOTUS rule and it has only gotten worse since.”

Sen. Tom Carper (D-Del.), the top Democrat on the Senate Environment Committee, said Trump’s order put the country’s streams and wetlands at risk of pollution.

“The only thing today’s executive order makes clear is that clean water is not a priority for the Trump Administration,” Carper said.

Hart Energy staff contributed to this report.