TORONTO -- Canada Post is replacing the locks on thousands of community mailboxes after an "unacceptable" number of customers had their mailboxes frozen shut last winter.

Spokesman Jon Hamilton says the locks on community mailboxes are being replaced in communities that include Ottawa, Montreal, Quebec's eastern townships, Bathurst, N.B., Halifax, Charlottetown and St. John's.

He says the postal agency began notifying customers about the lock replacement in September, advising them that the change would be coming.

Customers whose mailbox locks are being replaced are sent a new set of keys about two weeks before the change is made.

Hamilton says the lock replacement is now underway and the work will continue for the next few months.

He says Canada Post wants customers to continue to contact the Crown corporation if they have problems with their mailboxes because that's how the defective lock issue came to light.

"Last winter we had an unacceptable level of customers experiencing frozen locks, mainly in Eastern Canada," Hamilton said in an interview. "We're going back to those areas where we had issues and replacing the locks for the community mailboxes in those areas."

Hamilton noted that not everyone who will have their locks replaced experienced issues last winter, but Canada Post is nonetheless taking the action to prevent future problems.

"Rather than doing a one-off, whack-a-mole approach knowing that we've had some issues, we said let's go out and replace them and ensure that customers can have access to their mailboxes this winter," Hamilton said.

The previous problematic locks were particularly susceptible to freezing rain and flash freezes, Hamilton explained, but the new locks have been tested to withstand such conditions.

The lock replacement effort comes as Canada Post's community mailbox expansion plan is currently uncertain.

In the face of declining traditional mail volumes, the corporation had announced a plan in December 2013 to end door-to-door delivery and gave itself five years to implement the move to community mailboxes.

About 100,000 made the transition in 2014, and another 900,000 households were expected to switch to community mailboxes in 2015.

Prime Minister Justin Trudeau made a verbal promise, however, to "restore" door-to-door home mail delivery.

But so far, the Liberal government, which came into power a year ago, has committed only to stopping any further reduction in home delivery while it conducts a review of Canada Post's operations.