OTTAWA, May 10 (Reuters) - The Canadian government is moving to push back the start of a possible strike by railway workers at Canadian National Railway (CN) and Canadian Pacific Kansas City (CPKC), an official said on Friday.

Workers represented by the Teamsters union last week voted overwhelmingly to strike as early as May 22. Railways are critical to Canada's economy, due to its vast geography and exports of grain, potash and coal.

Late on Thursday, federal Labour Minister Seamus O'Regan said he had asked the Canada Industrial Relations Board to look at whether the strike might have safety implications. Until the board has issued a decision, the strike cannot start.

In an emailed statement, the Teamsters union said it was reviewing O'Regan's move and would "obviously comply with any order" from the board.

O'Regan acted after stakeholders expressed concern about the effect of a stoppage on healthcare infrastructure, in particular shipments of propane, which is used as a back-up generator fuel for rural hospitals, said the official, who requested anonymity given the sensitivity of the situation.

There is no set timeline for the board to issue a decision.

(Reporting by David Ljunggren, Editing by Franklin Paul)