Canada Post received a strike notice Monday from the union representing more than 55,000 postal workers, with operations poised to shut down by the end of the week — for the second time in six months.

The union informed management that employees plan to hit the picket line starting Friday morning at midnight, the Crown corporation said.

A work stoppage would affect millions of residents and businesses who typically receive more than two billion letters and roughly 300 million parcels a year via the service.

No new items would be accepted until the strike ends, while those already in the system would be “secured” but not delivered, Canada Post said. Social assistance cheques and live animals mark the two exceptions, with delivery of both continuing — though no new animals would be let through — it said.

A 32-day strike during peak shipping season ahead of the winter holidays last November and December left millions of letters and parcels in limbo and a massive backlog to sort through.

Canada Post said the disruption would deepen the company’s grave financial situation and argued both sides should focus on hammering out a deal.

“It’s disappointing. It’s just going to increase the level of concern for our employees, small businesses, charities, people who are counting on Canada Post,” said spokesman Jon Hamilton in a phone interview Monday afternoon.

“Large customers have already been moving their items out of our system, knowing that May 22 was coming,” he added, referring to the expiration of a pair of collective agreements that had been extended until this Thursday.

The Canadian Union of Postal Workers said Monday it issued the 72-hour strike notice “in part to respond to the employer’s recent indication that it may unilaterally change working conditions and suspend employee benefits.”

The union noted that the last work stoppage ended after the federal government stepped in with a ministerial directive, resulting in a labour board ruling that summoned the parties back to negotiations.

“There is still time to return to the bargaining table,” the union stated, stressing its goal remains new contracts, including for the 23,000 mail carriers.

The labour impasse comes amid broader questions about the future of Canada Post, which notched an $845-million operating loss in 2023.

On Friday, a federally commissioned report on the 158-year-old institution highlighted its flagging business model and recommended foundational changes, including phasing out daily door-to-door letter mail delivery for individual residences while maintaining it for businesses.

The 162-page paper by William Kaplan, who headed the commission, stated that moratoriums on rural post office closures and community mailbox conversions should be lifted as well.

“Canada Post is facing an existential crisis,” he wrote.

“My recommendations are based on my conclusion that there is a way to preserve Canada Post as a vital national institution. I have designed them to respond to the present problem: to arrest and then reverse the growing financial losses by putting into place the necessary structural changes both within and outside the collective agreements.”

The union largely rejected the report’s findings.

“What we have seen so far has left us disappointed — but not surprised,” said spokeswoman Siân Griffiths in an email.

“The union, band councillors, municipalities, international organizations — and the public — took the time to research and send in thorough submissions in our support. All were dismissed in the report. Instead, the report simply regurgitates Canada Post’s proposals and positions,” she argued.