Canada Post plans to close the office in North Sydney that handles undeliverable mail, workers learned Tuesday.

The union representing the workers said 13 people would be affected: 11 with the Public Service Alliance of Canada and two with the Canadian Union of Postal Workers.

But Canada Post disputes those numbers. It says there will be 10 affected employees, who will all be reassigned

Gordon MacDonald, the president of Local 117 of the Canadian Union of Postal Workers, told CBC News the announcement came as a shock.

"Here in North Sydney, we have an undeliverable mail office on King Street," he said.

"Canada Post has just slithered in here this morning, brought everyone together on the floor to announce the closure of this building to be moved to Scarborough, Ont."

"They have some provisions in their collective agreement for job security. CUPW workers will be absorbed in the Sydney operation as an over-complement," MacDonald said.

"With all the PSAC positions we just lost in Cape Breton, who knows where these people will end up."

MacDonald said the union was told once the King Street building is vacant, Canada Post will move its letter carriers — currently housed on Archibald Street — into the King Street building.

He said the union plans to fight the decision.

But Canada Post said this all comes down to the bottom line.

"Our employees in North Sydney – and across Cape Breton – have done a great job," said spokesperson Anick Losier in an e-mail to CBC.

"But we need to save costs, maximize our capabilities across the mail network and increase efficiencies across the country to maintain long-term service."

The undeliverable mail office is scheduled to close in December.