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 ( CNI ) and Canadian Pacific

Kansas City ( CP ) , 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.