CALGARY - Canadian Pacific Railway (CP.TO) says it has begun shutting down train operations ahead of a possible strike set to start Saturday by two unionized workforces.

The company says it has an embargo application in place on shipments going to or from CP's Canadian locations that will take effect just after midnight on April 21.

Canadian Pacific says it continues to bargain with both the Teamsters Canada Rail Conference and the International Brotherhood of Electrical Workers, which have given strike notices for this Saturday.

A spokesperson for the Teamsters Canada Rail Conference, which represents about 3,000 CP Rail engineers and conductors, said Thursday that less than two days from a strike deadline they had no progress to report.

The potential strike comes at a difficult time for the railway, which is under pressure from shippers to move backed-up grain shipments and supply more trains to the pipeline-constrained oil industry in Western Canada.

Both unions reached a tentative deal with Canadian National Railway Co. last month for new contracts for about 1,700 CN Teamsters workers and over 700 IBEW members.