Canada Post says it is doing its best to cope with a 40-million-letter backlog in the wake of the recent labour disruption, but the postal workers' union says it is being denied the overtime hours needed to get that mail delivered quickly.

The corporation said Wednesday that in addition to the eye-popping backlog, workers are also coping with an average of nine million more pieces of mail per day than they normally would be at this time of year.

Canada Post spokesperson John Caines said when the company re-opened for business on June 27 after nearly a month of rolling strikes and then a lockout, it was flooded with international mail, as well as letters Canadians had held back while waiting for the labour dispute to be resolved.

"So we are at capacity at most of our plants right now and it's going to take some time to get through that," Caines told CTV News Channel in an interview Wednesday evening.

Caines said the corporation aims to have the bottleneck cleared by the end of next week. To do that, he said, the company is offering overtime to workers at sorting facilities, including over the weekend, and allowing carriers to begin work one hour early to sort their mail in order to spend a full eight hours on their routes.

But the union says with a nine-hour cap on a mail carrier's day, there's not enough time to get all that mail delivered.

John Wastell, president of CUPW Kitchener-Waterloo Local 560, said on an average day with average mail volumes, it takes a carrier about eight hours to deliver all of his or her mail. With the current higher volumes, workers are being forced to return to the depot without finishing their work.

"Obviously it's taking the letter carriers a lot longer to do this," Wastell told News Channel. "And they're telling these carriers, ‘Sorry, when you get to a certain time on your wristwatch, you stop your delivery and you bring all your mail back with you regardless of where you are on your delivery route.'"

Wastell said in his region of Ontario, he has heard that some mail that had been sorted pre-lockout, which is supposed to be arriving in mailboxes first, has had to be re-processed. That combined with other glitches means "the backlog is growing, not shrinking."

Wastell and Montreal CUPW head Alain Duguay both questioned the corporation's timeline of having the backlog cleared by next week.

Duguay told CTV Montreal Wednesday he's never seen so much mail, including during the Christmas season, and predicted that "it's going to take months before we get back to normal."

Caines said the company cannot afford to pay more overtime after losing about $200 million during the labour disruption.

"We have to be fiscally responsible as we move forward too," Caines said.

Mail service resumed on June 27 after postal workers began a series of rotating strikes on June 3 that culminated in a lockout on June 14. The labour disruption followed months of fruitless negotiations between the union and the corporation on a new contract.

Members of Parliament stayed in Ottawa past the scheduled start of their summer break to debate, and ultimately pass, back-to-work legislation, despite a filibuster led by the NDP.

The corporation and the union will each submit a final contract offer to an arbitrator, who will determine which one forms the new deal.

With a report from CTV Montreal's Tarah Schwartz