Federal regulators are allowing work on the 600-mile Atlantic Coast Pipeline to expand in North Carolina.

Federal Energy Regulatory Commission officials this week approved work to proceed without further steps to protect endangered species. The FERC order issued Tuesday said work could be stopped to protect the environment if ordered by a federal court.

Opponents are trying to force a stop to the $6 billion project after a federal appeals court in Virginia in May vacated a U.S. Fish and Wildlife service approval meant to protect threatened or endangered species.

The pipeline being developed by Dominion Energy, Duke Energy and Southern Company will carry fracked natural gas from West Virginia through Virginia to North Carolina.