A helicopter lands near a test drilling site for Pebble Mine in Southwest Alaska in 2007. (Al Grillo/AP)

Environmental Protection Agency Administrator Scott Pruitt directed the agency’s staff Wednesday to craft a rule limiting the agency’s ability to preemptively halt projects on the grounds that they would pollute nearby waterways.

The instruction, which Pruitt outlined in a memo to the EPA’s office of water, takes direct aim at the authority the agency used in 2014 to block construction of a massive gold and copper mine near Alaska’s Bristol Bay because it could cause “significant and irreversible harm” to a wild salmon habitat.

The new approach would bar the EPA from invoking its power under the Clean Water Act before a permit application has been filed with the U.S. Army Corps of Engineers or a state, as well as after the corps or state authorities have issued a permit.

“Today’s memo refocuses EPA on its core mission of protecting public health and the environment in a way that is fair and consistent with due process,” Pruitt said in a statement. “We must ensure that EPA exercises its authority under the Clean Water Act in a careful, predictable, and prudent manner.”

It could take a year or longer to finalize any changes to how the EPA exercises its authority under Section 404(c) of the Clean Water Act, which has remained unchanged since 1979. Pruitt gave his staff six months to draft a rule and submit it to the White House Office of Management and Budget, and such a proposal would be subject to public comment before it could be finalized.

Mining industry officials and Republican lawmakers such as Senate Environment and Public Works Committee Chairman John Barrasso (Wyo.) praised the idea, while environmentalists described it as Pruitt’s latest attempt to roll back long-standing conservation policies.

“EPA’s action is a vital step forward in returning certainty and order to the permitting process in the U.S.,” National Mining Association spokeswoman Ashley Burke said in an email. “Even the mere threat of retroactive and preemptive veto actions has harmed America’s competitiveness when it comes to attracting investment in U.S.-based mining projects, adding volatile obstacles into what is already an extensive, established process at the state and federal levels.”

Northern Dynasty Minerals Ltd. filed a permit application with the Army Corps of Engineers in December to construct the Pebble Mine in the Bristol Bay watershed, and the agency began moving to undertake an environmental-impact statement.

While the regulatory climate has bolstered the chances of the controversial project winning federal approval, the mine now faces a huge economic challenge. The major investor, First Quantum Minerals Ltd., pulled out last month.

Officials at the Natural Resources Defense Council, an environmental advocacy group, said in interviews that Pruitt’s move has no immediate repercussions but could be significant over the long term.

Jon Devine, a senior attorney and the NRDC’s director of federal water policy, said the memo has little practical effect because Pruitt only directed his staff to start the long process of writing a rule.

“He could have accomplished the same thing by making a call from his soundproof phone booth,” Devine said. “The fact he’s making a big deal out of this ministerial action reflects his desperation in being seen as a go-getter in helping to eliminate environmental safeguards.”

But should Pruitt manage to finalize a rule along the lines that he noted in his directive, “that would be a terrible and very disruptive public policy,” one that could hamstring the EPA by creating a “very narrow window of time” during which the agency could act, Devine said.

Citing the Pebble Mine and a mountaintop mining project in West Virginia known as the Spruce Mine, he said: “We have textbook examples of why that’s a terrible idea. Basically, he’s going after his successors.”