The union representing more than 9,000 workers at Canada’s two biggest railways says public safety is at stake as contract negotiations ground to a halt this month, with a potential strike on the horizon.

On Friday, Canadian National Railway Co. CNR-T and Canadian Pacific Kansas City Ltd. CP-T asked the labour minister to appoint a conciliator for the bargaining process over a new collective agreement for train conductors, engineers and yard workers.

The notice of dispute starts the clock on a possible strike or lockout, which could occur as soon as 81 days after, in early May.

Teamsters Canada president François Laporte says the two railroad operators aim to scrap key rest provisions from workers’ contracts in a move that could increase crew fatigue and put public safety at risk.

CN says recent regulatory changes have made it harder to find crews and necessitated a “modernization of the compensation model.”

CPKC says it has been negotiating in good faith since September and offered compensation boosts and more schedule predictability, but that the railway and the union “remain far apart on the issues.”