The Environmental Protection Agency said it would block construction of a controversial copper and gold mine in Alaska that has brought intense lobbying and congressional scrutiny in a move that industry officials say amounts to an illegal, "pre-emptive" action.

The EPA said Friday that it would use its Clean Water Act authority to bar developers of the proposed Pebble Mine from obtaining a permit to build it in Bristol Bay in southwest Alaska. The agency said the mine would disturb Bristol Bay's vibrant sockeye salmon -- it hosts nearly half the world's population -- as well as native tribes and commercial fishermen.

“Extensive scientific study has given us ample reason to believe that the Pebble Mine would likely have significant and irreversible negative impacts on the Bristol Bay watershed and its abundant salmon fisheries,” EPA Administrator Gina McCarthy said. “It’s why EPA is taking this step forward in our effort to ensure protection for the world’s most productive salmon fishery from the risks it faces from what could be one of the largest open pit mines on earth."

The EPA ruling could invite legal action from the mine's supporters, as the industry has contested whether EPA can reject the necessary permit. That's because developer Northern Dynasty, through the Pebble LP, has yet to submit a formal blueprint to EPA.

The mine's boosters have pointed to a similar case in which the EPA "retroactively" repealed a permit for a strip-mining operation in West Virginia, a case that industry and more than two dozen states are pressing the Supreme Court to pick up.

Groups such as the National Association of Manufacturers, with congressional Republicans, have said the step the EPA proposed taking Friday is illegal because it is working with a "hypothetical" mine scenario. They contend such a ruling would spook investment near waterways.

“When it comes to the Pebble Mine, EPA has shown that they are willing to disregard due process and lawfully established permitting procedures to ensure the failure of any project like this. EPA’s desperate attempt to kill a potential mine should signal a major red flag to businesses,” said Sen. David Vitter, R-La., the top Republican on the Senate Environment and Public Works Committee.

The mine's opponents — which include congressional Democrats, environmental groups, commercial fishermen and native tribes — and the EPA, however, say the agency has plenty of information with which to work. The agency based its studies on Securities and Exchange Commission filing submitted by Pebble LP.

An EPA environmental review released in January said the mine's footprint would destroy between 24 and 94 miles of streams and two to eight square miles of wetlands that are vital habitats for sockeye salmon. That would endanger an ecosystem that generated $480 million in 2009, largely from commercial fishing.

“The science EPA reviewed paints a clear picture: Large-scale copper mining of the Pebble deposit would likely result in significant and irreversible harm to the salmon and the people and industries that rely on them," said Dennis McLerran, the regional EPA administrator for the Pacific Northwest and Alaska.

Environmental and commercial fishing groups, which have ramped up lobbying activities through the past year, cheered the decision.

"It is difficult to overstate the significance of this announcement. If the EPA follows the science and follows through on this, it will rank as one of the most significant conservation achievements of the past 50 years," said Chris Wood, chief executive of Trout Unlimited.