CHICAGO — Amtrak is canceling some of its long distance trips from Chicago starting Tuesday, ahead of a possible freight rail union strike.

Amtrak is suspending routes between Chicago and San Francisco, Los Angeles and the Pacific Northwest.

Parts of a fourth route from Chicago between LA and San Antonio are also suspended. Amtrak says the adjustments are necessary to avoid stranding passengers.

Freight rail workers are seeking higher pay, more paid leave time and better working conditions.

Amtrak operates nearly all of its trains on tracks owned and operated by freight railroads.

Metra says four of its lines would have to be suspended. Five others are in question if a strike happens.