A possible strike by freight rail workers began to disrupt the nation’s passenger rail Monday, while potentially rattling commutes and cross-country travel for thousands of Americans if a strike isn’t averted.

Amtrak announced Monday that interruptions will begin Tuesday on its national network. The passenger railroad said it is pulling trains on three long-distance routes “to avoid possible passenger disruptions while on route.”

“These initial adjustments … could be followed by impacts to all Long Distance and most State-Supported routes,” Amtrak said in a statement. “These adjustments are necessary to ensure trains can reach their terminals prior to freight railroad service interruption if a resolution in negotiations is not reached.”

Amtrak owns and operates much of its own track in the busy Northeast Corridor between Washington and Boston, but elsewhere it crosses the country on tracks owned by freight lines. Commuter lines that run between major cities and suburbs often operate on a similar model. Those freight tracks likely wouldn’t be available to passenger trains in the event of a widespread strike.

Any disruption would affect a passenger rail industry already weakened by 2-1/2 years of the pandemic, which has hit commuter rail lines especially hard.

Amtrak said it is closely monitoring the labor negotiations and is “hopeful that parties will reach a resolution,” citing potential effects on passenger operations. Amtrak said it has begun phased adjustments to service in preparation for a possible freight rail service interruption later this week, adding that “such an interruption could significantly impact intercity passenger rail service.”

Amtrak Monday announced cancellations on trains with Tuesday departures on the Empire Builder, the California Zephyr and the Southwest Chief routes.

Most travel within the Northeast Corridor would not be affected, Amtrak said. However, minor schedule changes are expected on a small number of Northeast Regional trains serving destinations from Virginia to Boston. The company will let passengers change their reservation for free for departures scheduled through Oct. 31.

Jim Mathews, president and chief executive of the Rail Passengers Association, said cancelling trains early in the week makes sense to avoid a scenario in which rail passengers could become stranded.

“It’s better to cancel some trains now than to send some people out onto the road and then have them stranded in the middle of nowhere because the strike has hit and the train can’t move anymore,” he said. “Meanwhile we all keep our fingers crossed that finally (the railroads and labor unions) get to a settlement.”

Freight railroads and unions representing their workers have been locked in a lengthy dispute over pay and working conditions. After a presidential board recommended a compromise, 10 of 12 unions involved in the talks have signed on to the deal, but the two largest have not. A cooling-off period ends Thursday night, after which workers could strike or the railroads could lock out passenger rail agencies.

Officials at several regional rail agencies said Monday they were holding internal meetings to determine the potential effects and to develop contingency plans. A strike is not certain and the scope of any disruption to passenger services was not clear.

A key question would be whether the freight railroads’ dispatchers – whose job is to route trains – would continue to work. Without them, passenger trains probably could not operate on freight tracks.

Metrolink, a network of seven lines serving Los Angeles and other Southern California communities, warned customers last week of the potential for disruptions. Scott Johnson, a spokesman for the agency, said five of its seven lines use tracks owned by freight railroads, meaning as many as 70 percent of its customers could be affected.

Yet Johnson said Metrolink had little information Monday about what the precise effects might be.

“We are largely working from a position of darkness,” he said.

Normally when Metrolink cancels trains, Johnson said it organizes buses as a replacement. But in the case of a strike, the agency does not expect it would be able to provide an alternative means of transportation.

“Because of the possible expansive nature and the high number of trains, there simply are not enough buses to provide alternative service,” Johnson said.

The Maryland Department of Transportation said Monday that freight railroad CSX had notified it about the potential for a strike beginning Friday. The state said a strike would result in the “immediate suspension” of all service on two of its three MARC commuter lines serving the District – one to Baltimore and another to Martinsburg, W.Va.

Not every commuter rail operation would be affected. RTD, the transit agency serving Denver, said it didn’t expect its lines to suffer in the case of a strike. The nation’s biggest transit operator, New York’s MTA, said its two commuter rail services also were not expected to be affected.

The looming rail labor strike could further snarl a national rail network that’s been slowing to a crawl for months, officials with the Rail Passengers Association said, particularly hurting Amtrak passengers.

Disruptions to intercity train operations are on the rise, and more are likely as uncertainties linger amid staffing shortages and increased demand. Amtrak trips have been hampered by worsening problems on freight rail lines, which often share tracks with Amtrak trains.

One-third of Amtrak customers encountered delays in July, according to on-time performance data, with an average delay of 71 minutes. The share of delayed customers is trending up, Amtrak data shows, and delays are getting longer.

The disruptions are more pronounced for travelers on long-distance routes – which are late more than half the time – and in parts of the country outside the Northeast Corridor. Railroad association officials said the dispute could result in more widespread late trains or cancellations.

Commuter rail operators have been hard hit by changing working patterns brought on by the pandemic. In many cases, they offer more limited service at rush hour, which no longer suits workers with more flexible schedules. In Los Angeles, for example, Johnson said Metrolink had about 40,000 weekday boardings before the pandemic, a figure that now stands at about 17,000.