NEAR WINTERGREEN, Va. — The Appalachian Trail is barely a footpath at some points on this mountain ridge, marked mainly by white patches on trees. But the humble walkway has become a major barrier to an $8 billion natural gas pipeline. On Monday, the U.S. Supreme Court will consider which one should prevail.

The Atlantic Coast Pipeline begins in West Virginia and is planned to cross some of the most mountainous scenery in central Virginia before completing its 600-mile path in North Carolina.

Work in Virginia has been halted for more than a year as the builders contend with a host of setbacks handed down by federal courts. None is more crucial than the question of whether the U.S. Forest Service has authority to grant the pipeline right of way under the Appalachian Trail in the George Washington National Forest.

Judges from the U.S. Court of Appeals for the 4th Circuit threw out a Forest Service permit in December 2018, saying federal law prohibits any agency from allowing a pipeline on “lands in the National Park System.” That includes the trail, the judges said.

The pipeline’s builders, led by Dominion Energy, appealed to the high court, saying the ruling could create an impenetrable wall along the trail’s course from Georgia to Maine.

“Simply put, there is no basis in any federal statute to conclude that Congress intended to convert the Appalachian Trail into a 2,200-mile barrier separating critical natural resources from the eastern seaboard,” lawyer Paul Clement wrote in a brief on behalf of the pipeline.

The plaintiffs note that pipelines already cross the trail at 34 locations.

The Trump administration has weighed in on behalf of the project, with Solicitor General Noel Francisco arguing that while the National Park Service administers the trail, the land beneath it is controlled by the Forest Service.

Environmentalists opposing the construction argue that no pipeline has been granted a right of way across the trail on federal land since it became part of the park system. Other crossings are on private or state lands or on easements that predate federal ownership.

Trying to separate the land from the trail is an “elusively metaphysical distinction” that “contradicts the government’s own long-standing approach to administering the Trail,” according to a brief from lawyer Michael K. Kellogg, who will argue for the environmental groups in Monday’s hearing.

Virginia Attorney General Mark R. Herring (D) has filed a brief on behalf of the project’s opponents, arguing that the pipeline threatens “several of Virginia’s most cherished places.” Herring also questions whether there is any economic need for the pipeline, noting that “the demand for natural gas will remain flat or decrease for the foreseeable future and can be met with existing infrastructure.”

The high court’s ruling could determine the fate of the Atlantic Coast Pipeline, a controversial project that has drawn national attention from environmentalists, including former vice president Al Gore. Approved by the Federal Energy Regulatory Commission in 2017, the pipeline initially was projected to cost about $5 billion but has ballooned in price with multiple delays.

Fourth Circuit judges struck down a number of the project’s permits for being awarded hastily and improperly. Earlier this year, the court threw out a state permit for a pumping station in a historic African American community in Buckingham County, Va., saying the builders failed to consider whether the facility would unduly harm a minority group.

The ruling on the Appalachian Trail crossing had three other elements that are not part of the appeal to the high court. The judges also said the permit didn’t comply with mandatory standards for protecting soil, water and wildlife; that the agency didn’t take a hard enough look at landslide and erosion risk; and that the Forest Service rejected alternate routes without fully analyzing them.

Federal law requires considering the feasibility of other routes before approving a pipeline crossing in a national forest.

A spokeswoman for Dominion said the company is working with federal agencies on all three of those elements and is confident it can address them.

The site where the pipeline would meet the trail is west of Charlottesville on the edge of George Washington National Forest. The builders want to tunnel through a mountain some 700 feet below the level of the trail, which runs along the ridgetop and intertwines with the Blue Ridge Parkway.

“The pipeline will be completely invisible from that crossing,” Dominion spokeswoman Ann Nallo said. “This project, even from the start, has always been designed with the environment in mind.”

Opponents concede that the crossing itself won’t physically affect the Appalachian Trail but say the pipeline and its long approach to the mountain will change the landscape.

Just north of the tunnel, the trail emerges onto a rocky outcrop at Cedar Cliffs, with a spectacular view of the Shenandoah Valley far below. The pipeline route would march across the valley, threading past farms and villages and then slicing through an unbroken tract of the national forest.

Even though the pipeline is underground, it would have a 50-foot-wide cleared path along its length.

“It will be very visible,” said Lynn Cameron, a board member for the Virginia Wilderness Committee, one of the plaintiffs in the case.

“It’s hard to separate the Appalachian Trail from the scenic beauty that hikers come here to see,” she said, standing on a lichen-covered rock and gesturing down at the bare stretch of forest, streaked with pockets of evergreens. “Some of the best tracts of Appalachian Trail are through national forest land. That’s what makes this route particularly painful.”

Greg Buppert, a lawyer with the Southern Environmental Law Center, accused Dominion of pushing the approval process too aggressively. “This is a protected landscape,” he said. “I think the problems we’re seeing with the pipeline are self-inflicted problems.”

Nallo countered that the company has gone to great lengths to satisfy environmental concerns. The pipeline’s pathway will be covered with grass and native plants, she said, adding that much of the landscape is already altered by human activity.

“I visited the trail a couple of times,” Nallo said. “You’re very close to the Blue Ridge Parkway at that point. When the leaves were down, I could see some of the houses and the roads down in the valley. . . . I think it’s a good example of how we try to achieve that balance as humans of being able to enjoy nature but being able to use those areas.”

The consolidated cases the Supreme Court will hear Monday are U.S. Forest Service v. Cowpasture River Assn. and Atlantic Coast Pipeline LLC v. Cowpasture River Assn.