The International Brotherhood of Electrical Workers (IBEW), which represents about 750 CN Rail employees, says signal and communication workers have walked off the job across the country.
Workers were legally on strike as of 11 a.m. local time on Saturday.
The IBEW gave a 72-hour strike notice Wednesday morning.
A spokesman for CN Rail says the company has implemented an "operational contingency plan," noting that operations are continuing "safely and at normal levels."
CN Rail says it continues to encourage the union to resolve sticking points on wages and benefits through binding arbitration.