OTTAWA, Ontario (AP) -- The Canadian Union of Postal Workers on Thursday declared a countrywide strike at the national postal service, hours after the federal government announced that door-to-door mail delivery would end for nearly all households within the next decade.

Procurement Minister Joël Lightbound announced sweeping changes aimed at shoring up Canada Post's finances in response to a decline in letter mail and the government corporation's small share of the parcel market.

The changes include more community mailboxes and slower delivery times.

The union said it was caught off-guard by the changes and argued Canada Post and the government are creating the conditions that drive down demand for its letter and parcel services.

CUPW said all of its Canada Post members are on strike "effective immediately," adding the corporation has avoided "real bargaining."

The office of Jobs Minister Patty Hajdu did not immediately respond when asked for comment.

Lightbound said earlier the government will accept all of the recommendations of a commission of inquiry which called for the introduction of more community mailboxes.

"Canada Post is a national institution, older than our country itself, that has been serving Canadians for more than 150 years," Lightbound said. "For generations, postal workers have connected communities in every corner of the country, providing an essential lifeline to hundreds of northern, Indigenous and rural communities."

At the same time, he said, the service is facing "an existential crisis" and "repeated bailouts from the federal government are not the solution."

The change to mail delivery is expected to increase the time it takes Canada Post to deliver letter mail from an average of three to four days to an average of three to seven days.

Four million Canadians will also see their service switch from door-to-door delivery to a community mailbox model, and some post offices will be closed for good. Lightbound said that change could generate $400 million Canadian (US$287 million) per year in savings.

Lightbound said more than three in four households don't have door-to-door delivery now, but there has been a moratorium in place on expanding the use of community mailboxes. That moratorium is ending.