Canada Post said it has issued a 72-hour lockout notice to the Canadian Union of Postal Workers (CUPW), raising the spectre of a work stoppage by Friday.

Management said it plans to suspend the collective agreement as of Friday. It blamed prolonged negotiations, the union’s strike mandate and the financial cost of a rapid decline in mail volume.

Canada Post said the 72-hour notice does not necessarily mean it will shut down on Friday saying the measure would allow it “take measures that are necessary to respond to the changing business reality.”

CUPW said the corporation is using the lockout notice to drive 50,000 workers “out onto the streets without pay in an effort to impose steep concessions on them.”