The union representing CN signal and communication workers has reached a tentative agreement with the railway to renew the labour contract for some 700 employees in Canada.

The announcement, made in a press release Monday, says details of the agreement are being withheld until it can be ratified by a vote of the union's members. The results of that vote are expected in May. 

Earlier Monday, Metrolinx spokesperson Anne Marie Aikins said a possible strike could affect three lines — Lakeshore West, Richmond Hill and Kitchener — because the lines are owned by the railway. 

"We've been working very closely with CN, and in the event of a labour disruption, we do expect that we will be able to operate normally. The CN signal system would continue to operate and we will work closely with them to manage any issues that could arise," she said, ahead of the agreement.

CN Rail

The International Brotherhood of Electrical Workers represents more than 700 signal and communications workers in Canada. (CBC)

The International Brotherhood of Electrical Workers System Council No. 11, which represents more than 700 signal and communications employees in Canada, served strike notice on Friday. It was to take effect at 12:01 a.m. Tuesday.

Before the agreement, ​Patrick Waldron, spokesperson for CN Rail, said in an email that talks were continuing.

"We still believe a fair agreement can be reached before the strike deadline and we are committed to working with the union as long as necessary," he wrote.

"CN has made contingency plans to continue rail operations in the event of a strike and will maintain service to our freight customers and passenger operations along CN lines."

Notice of the strike was served because CN refused to agree with the union to extend conciliation, said Steve Martin, senior general chairman of the union local said. Ninety-nine per cent of members voted in support of a strike, he said.

"We were left no other choice except to file the notice to strike to ensure we can continue protect the rights of our members," Martin said in a news release  Saturday.

The collective agreement between the union and railway expired on Dec. 31, 2016 and both parties have met five times with "only minimal progress," Martin said. Several issues remained outstanding, he said.

The union represents the workers who install and maintain signals and trackside equipment for railways in Canada. Members also install and maintain the warning systems used at railway highway crossings.