The Federal Energy Regulatory Commission on Tuesday ordered that all work on the Mountain Valley Pipeline stop except stabilization and restoration activities.

The order, outlined in a Tuesday letter from FERC’s Office of Energy Projects, follows on the heels of a federal appeals court ruling Friday that pressed pause on a key permit for the 300-hundred natural gas pipeline from West Virginia into Pittsylvania County issued by the U.S. Fish and Wildlife Service until further review can be conducted.

“Construction activity along all portions of the project and in all work areas must cease immediately, with the exception of restoration and stabilization of the right-of-way and work areas, which commission staff believes will be more protective of the environment, including listed species, than leaving these areas in an unstable condition,” the letter stated.

At the heart of the conflict surrounding the U.S. Fish and Wildlife Service permit are four endangered or threatened species: two freshwater fish known as the candy darter and Roanoke logperch, the Indiana bat and the northern long-eared bat.

In recent months pipeline opponents have concentrated their efforts on the permit (known as the biological opinion and incidental take statement) for the project, which developers say is about 90 percent complete. In August, shortly after the Sierra Club asked the Fish and Wildlife Service to revoke the permit, Mountain Valley voluntarily suspended all construction activities that could harm the four target species. FERC subsequently notified the project developers that it was reopening its review of the pipeline’s impacts on these species but did not order that work be stopped.

Friday’s decision by the U.S. Court of Appeals for the 4th Circuit stayed the permit until completion of consultation between FERC and the Fish and Wildlife Service.

Mountain Valley Pipeline spokeswoman Natalie Cox said the developer “will continue to work closely with all agencies to resolve these issues as quickly as possible.”

“While we understand the FERC needing to take this action, much of MVP’s forward-construction work was already deferred in accordance with MVP’s August 15, 2019, voluntary suspension or has been largely winding down for the winter season,” she said in an email.

David Sligh, conservation director for Wild Virginia, said FERC has previously allowed work that “is clearly construction” to be done under the guise of stabilization.

“The commission must now act responsibly and clearly prohibit all activities that are not absolutely necessary to protect the environment for the entire project. FERC must no longer play deceptive games that allow further destruction from a project that cannot protect our resources and may never be completed,” he said.