In a complaint filed on Aug. 29, Amtrak said it wants the Surface Transportation Board (STB) to investigate CN for causing delays on its Illini and Saluki lines, which travel on CN-owned track between Chicago and Carbondale, Illinois.

A spokesman for Montreal-based CN said that the company would respond to Amtrak's investigation request, but had no further comment.

Amtrak said that under federal law, intercity passenger trains have a right to dispatch preference before freight trains. If that right was violated, Amtrak has asked the STB to award damages and other relief.

On-time performance of the Illini/Saluki service was 49 percent in the quarter ended June 30, Amtrak said, and 42 percent for the previous quarter.

Under the Passenger Rail Investment and Improvement Act, the STB must investigate an Amtrak complaint when on-time performance of intercity passenger trains falls below 80 percent for two consecutive quarters, Amtrak said.

Amtrak said it first filed a complaint about CN's performance in January 2012, but proceedings were stayed while the companies attempted to resolve the issue.

(Reporting by Susan Taylor, editing by G Crosse)