Canadian Teamsters and CP Rail blamed each other for a work stoppage Sunday that halted trains across Canada and interrupted shipments to and from the U.S.
More than 3,000 CP Rail conductors, engineers, train and yard workers represented by the Teamsters Canada Rail Conference are off the job after negotiators failed to reach a deal by a midnight deadline.
Both sides say they are talking with federal mediators.
Canadian Pacific covers much of the U.S. Midwest and is a large shipper of potash and fertilizer for agriculture.
It also carries grain from the U.S. to Canada.