Canadian National Railway union members have given strike notice ahead of a Tuesday deadline.
A strike would affect 3,200 conductors, trainpersons and yardpersons.
The Teamsters Canada Rail Conference warned in October it was prepared to launch job action after more than six months of unsuccessful talks.
The union provided the 72-hour notice Saturday as contract negotiations continue over the weekend.
The company says its offer to enter into binding arbitration was declined by the union.
The workers, who are mostly located in major urban centres across Canada, have been without a contract since July 23.
