President Donald Trump signed an executive order Tuesday rolling back the Waters of the United States rule, a 2015 environmental regulation that expanded the types of waterways to be protected by the federal government. It is one of Trump’s first major steps in dismantling Obama-era environmental protections.

The executive order instructs the Environmental Protection Agency and the Army Corps of Engineers to begin reviewing and revising the Waters of the U.S. rule to “ensure it promotes economic growth and minimizes uncertainty,” CNN reported. It also orders the Justice Department to request that federal courts place a hold on legal challenges to the rule while the review is underway, according to Reuters.

The Waters of the U.S. rule, or WOTUS, has faced intense legal and political opposition since its release two years ago. The U.S. Clean Water Act of 1972 gave federal authorities the power to regulate pollution in “navigable waters.” WOTUS expanded protection to include smaller streams and wetlands that drain into major rivers, bays, and drinking water sources. But farmers, the energy industry, developers, and Republican lawmakers have argued that the rule places too many restrictions on what landowners can do on their property. The Court of Appeals for the Sixth Circuit put the rule on hold in 2015 to allow several lawsuits to make their way through the court system. One such lawsuit was led by Scott Pruitt, the former attorney general of Oklahoma and the new administrator of the EPA. He will be in charge of revising the rule under Trump’s executive order.

Legal experts say it could take years for the Trump administration to dismantle the Waters of the U.S. rule. Any new rule will also be subject to a public comment period.