(Adds analyst comment, latest share price)
July 11 (Reuters) -
U.S. energy company Equitrans Midstream said on Tuesday it is evaluating all legal options, including an emergency appeal at the U.S. Supreme Court, after an appellate court halted construction of the West Virginia-Virginia Mountain Valley natural gas pipeline in the Jefferson National Forest.
Shares of the company were down about 4.6% to a six-week low of $8.77 on Tuesday after the U.S. Court of Appeals for the Fourth Circuit on Monday accepted arguments from groups opposed to the project that construction should stop as the court reviews federal approvals that allowed work to begin.
"Unless this decision is promptly reversed, it would jeopardize Mountain Valley's ability to complete construction by year-end 2023," the company said in a statement.
Mountain Valley is one of several U.S. projects delayed by regulatory and legal fights with environmental and local groups in recent years.
The pipeline received authorization from the country's energy regulator last month to restart construction and is key to unlocking more gas supplies from Appalachia, the nation's biggest shale gas-producing basin.
Federal approval for the 303-mile (488-km) project was placed into the text of the Fiscal Responsibility Act, which ended the debt ceiling crisis.
Even though the Fourth Circuit decision is "only applicable to the three miles (4.8 kilometers) of the Jefferson Forest," analysts at Height Capital Markets, an investment banking and research firm, said in a note that the decision could jeopardize a 2023 in-service date.
Mountain Valley is owned by units of Equitrans, the lead partner building the pipe, NextEra Energy, Consolidated Edison, AltaGas and RGC Resources.
When Mountain Valley started construction in February 2018, Equitrans estimated the 2.0-billion cubic feet per day project would cost about $3.5 billion and enter service by late 2018. (Reporting by Sourasis Bose in Bengaluru and Scott DiSavino and Clark Mindock in New York; Editing by Nivedita Bhattacharjee and Chizu Nomiyama)