A federal appeals court has refused to revisit a ruling that struck down a key permit for a proposed natural gas pipeline running through Virginia and West Virginia.

The 4th U.S. Circuit Court of Appeals said Friday that it would not revisit a February ruling by a three-judge panel that invalidated the U.S. Fish and Wildlife Service’s opinion that the Mountain Valley Pipeline would not jeopardize two endangered fish species.

The panel found “serious errors” with the agency’s conclusion that construction of the pipeline wouldn’t pose a threat to the Roanoke logperch or the candy darter.

The February ruling came one week after the same three-judge panel rejected a permit that would have allowed the pipeline to pass through a 3.5 mile (5.6 kilometer) section of the Jefferson National Forest. In both cases, the judges faulted the U.S. Forest Service and the wildlife agency for failing to adequately assess the pipeline’s environmental impact.

The 303-mile (487-kilometer) pipeline, which is mostly finished, would transport natural gas drilled from the Marcellus and Utica shale formations through West Virginia and Virginia.

The Roanoke Times reports that Mountain Valley now has little hope of obtaining the required approvals without going through a renewed permitting process. The $6.2 billion infrastructure project has been targeted by about a dozen environmental groups and is already more than three years behind schedule.

While acknowledging a “greater degree of uncertainty” following Friday’s court decision, a spokeswoman for Mountain Valley told the newspaper that its plans are still alive.