The U.S. Postal Service says it will indefinitely suspend deliveries of international mail to Canada due to a strike by the Canadian Union of Postal Workers.

Canadian officials have indicated the country cannot process mail from the U.S. while the strike is underway.

The suspension means several classifications of mail cannot be delivered, including Priority and First-Class Mail International and First-Class Package International Service.

The USPS has asked customers to wait to send any mail destined for Canada until further notice.

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The Canadian Union of Postal Workers began a strike in mid-November after union representatives and the Canadian government were unable to reach a new agreement over working conditions and compensation. The strike currently affects about 55,000 union members.

While the strike is underway, mail and parcels have not been delivered. Canada Post has warned customers to expect delays.

Canada Post says talks stalled in late November. On Sunday it presented a new framework that it hoped would help negotiations resume.

"The framework includes proposals to bring greater flexibility to the Corporation’s delivery model, while also demonstrating movement on other key issues. It is our hope that these proposals will reignite discussions and, together with the support of mediators, help the parties work toward final agreements," the agency wrote.