Metrolinx is warning GO Train commuters that a looming rail strike could result in significant delays starting Wednesday morning.

If the strike occurs, trains on the service's Barrie, Milton and Hamilton corridors will be at risk of the delays, said Metrolinx spokesperson Anne Marie Aikins.

Those lines are serviced by Canadian Pacific Railway workers, whose unions have signalled an intent to strike beginning at 10 p.m. Tuesday.

"We're warning our customers that the potential for delays is certainly there," Aikins said.

Metrolinx says GO Train service will only be affected in the event of signal or switching issues along those lines.

Under normal working conditions, CP Rail workers are able to repair the problems "fairly quickly," Aikins said.

However, if those workers strike, it will be up to CP Rail management to respond to malfunctions.

"They've assured us they can do that, but it may take them longer to get to an area to fix it," Aikins said of CP management.

"During rush hour that could back up trains significantly," she added.

Metrolinx spokesperson Anne Marie Aikins says the track problems will take longer to resolve during a potential strike. (Barry Smith/CBC)

Metrolinx says it had hoped to dispatch its own employees to the CP Rail lines during a potential strike, but an agreement could not be reached.

The provincial transit agency said other GO Train lines will not be affected.

In addition to possible commuting delays, a rail strike is also expected to shut down freight service across Canada.

Weekend negotiations fail

The unions representing train operators and signalling workers — the Teamsters Canada Rail Conference and the International Brotherhood of Electrical Workers — gave the railway notice over the weekend about its intent to strike.

The Calgary-based railway said it would keep meeting with union representatives, but the unions have accused the company of "refusing to negotiate seriously."

Employment Minister Patty Hajdu and federal mediators met with both sides this weekend but were unable to help them reach a new deal.

"I urge all parties to continue their hard work to reach a fair deal that avoids any disruption in service," Hajdu said Monday.

Ottawa has not discussed the possibility of back-to-work legislation should the strike drag on.

If a strike occurs it would be the third CP Rail strike since 2012.