President Donald Trump has signed an executive order mandating the review of a rule aimed at protecting small streams and wetlands from development and pollution.
Trump said at a White House signing ceremony that the rule is one of the "worst examples of federal regulation" and that "it has truly run amok."
He also said the rule has been "a disaster."
The order instructs the Environmental Protection Agency and the U.S. Army Corps of Engineers to review the Obama-era rule that redefined which bodies of water are protected under the Clean Water Act.
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Trump had railed against the rule during his campaign and Republicans have been fighting it since its inception, slamming it as an example of federal overreach.
But Democrats have argued that it safeguards drinking water for millions of Americans and clarifies confusion about which streams, tributaries and wetlands should be protected in the wake of decades-long uncertainty despite two Supreme Court rulings.
The order Trump signed also instructs the agencies to ask the attorney general to suspend ongoing court action while the review is underway. Implementation of the rule has been held up in court due to pending legal challenges.
The president has promised to dramatically scale back regulations that he says are holding back businesses, and has signed several orders aimed at that goal.
The League of Conservation Voters issued a pre-emptive statement slamming the move.
"This executive order is about one thing: protecting polluters at the expense of our communities and their access to clean drinking water," Madeleine Foote, the group's legislative representative, said in a statement.