OTTAWA (Reuters) - The Canadian Teamsters union, which is negotiating a contract with the country's two largest rail companies, on Friday said a work stoppage could start on Aug. 22 if a deal is not reached.

"The Teamsters will provide 72 hours advance notice in the event of any strike action," it said in a statement.

The union, Canadian National Railway and Canadian Pacific Kansas City agreed last week to restart stalled contact talks with the aid of a federal mediator.

(Reporting by David Ljunggren; Editing by Chris Reese)