An appellate court in Virginia on July 10 halted construction of the pipeline, which would run through the Jefferson National Forest.

The pipeline, which had received authorization from the Federal Energy Regulatory Commission last month to restart construction, is considered key to unlocking more gas supplies from Appalachia, the nation's biggest shale gas-producing basin.

Mountain Valley is owned by units of energy company Equitrans Midstream, the lead partner building the pipe; NextEra Energy, Consolidated Edison, AltaGas and RGC Resources.

(Reporting by Timothy Gardner; Writing by Richard Valdmanis; editing by Jonathan Oatis)