UNDATED (WOOD) — Amtrak is canceling three long-distance routes amid concerns that a contract dispute between unions and freight rails could lead to a strike.

The Southwest Chief between Chicago and Los Angeles, the Empire Builder between Chicago and Seattle, and the California Zephyr between Chicago and Emeryville, California (near San Francisco) stopped running starting Tuesday.

The Texas Eagle will also stop running its leg between Los Angeles and San Antonio.

“Amtrak is closely monitoring the ongoing freight rail – rail labor contract negotiations,” the company said in a statement. “While we are hopeful that parties will reach a resolution, Amtrak has now begun phased adjustments to our service in preparation for a possible freight rail service interruption later this week.”

Amtrak stressed that it and its workers are not involved in the labor dispute, which involves exclusively freight trains and not passenger trains, but explained that its trains run on freight lines in the Midwest, Southwest and West. A strike could begin Friday if negotiations don’t yield a deal. If that happens, Amtrak said more long-distance routes and state-supported routes could be affected.

Amtrak runs on its owns lines in the Northeast, so travel there should stay the same.