Mail delivery across Canada came to a standstill Thursday evening as members of the Canadian Union of Postal Workers (CUPW) launched a strike in protest against proposed federal changes to Canada Post.

The strike follows more than a year of tense negotiations between the union and the Crown corporation, which have yet to produce an agreement.

In response, Canada Post announced Friday it was reassessing the global offers it had prepared for the union, citing the federal government’s newly introduced “significant transformation changes.”

“We remain committed to reaching negotiated agreements with CUPW that are affordable, support our people, and help build a sustainable future for the company,” a spokesperson said.

The strike raises uncertainty for millions of Canadians who rely on postal services for essential deliveries.