SAINT JOHN, New Brunswick – J.D. Irving Limited, the parent company of lumber, oil and trucking companies in much of Canada and Maine, has decided to limit the U.S. operations of one of its three major trucking lines.

Mary Keith, an Irving spokeswoman, said Monday that the company’s RST Industries trucking line will end point-to-point shipments within the United States on March 20.

RTS will continue to handle shipments between the United States and Canada, Keith said.

The decision means that five salespeople in RTS’ Portland office will be laid off.

Another 20 truck drivers from across the state, Keith said, will be offered other jobs within Irving companies.

The termination of U.S. service and the closing of the Portland office, Keith said, “was the result of a downturn in market demand” for the trucking line’s services.

RTS was incorporated in 1970 and began operations in the United States in 1985.

The trucking line specializes in transporting petroleum, chemicals and food-grade edible oils. Irving owns a number of other trucking lines, including Sunbury Transport and Midland Transport.