WINNIPEG, Manitoba (Reuters) - Thousands of railway workers in Canada at Canadian National Railway and Canadian Pacific Kansas City have voted overwhelmingly to strike as early as May 22, the union said on Wednesday.

Railways are critical to Canada's economy, due to its vast geography and exports of grain, potash and coal.

Contracts covering locomotive engineers, conductors and yard workers at CN and CPKC expired on Dec. 31, 2023, and Teamsters Canada Rail Conference is re-negotiating a third agreement covering CPKC rail traffic controllers.

The three worker groups, numbering 9,300 workers, each voted over 95% to authorize a strike.

The sides have made no progress in six months of negotiations, said Teamsters Canada president Paul Boucher, adding that the companies were trying to remove rest provisions that are critical to safety.

CN said in a statement that the union has opposed moving toward a more modern agreement based on an hourly rate and scheduling changes.

CPKC said the parties remain far apart and now begin a mandatory 21-day period of federal mediation.

(Reporting by Rod Nickel in Winnipeg, Manitoba and David Ljunggren in Ottawa; Editing by Kirsten Donovan)

By Rod Nickel and David Ljunggren