Federal Labour Minister Patty Hajdu says the federal Liberals have given the House of Commons notice that they're prepared to legislate Canada Post employees back to work.

Hajdu says 48 hours' notice is required before introducing back-to-work legislation, but insisted that having done so doesn't mean the government will make the move to end rotating strikes by the Canadian Union of Postal Workers.

"We have complete flexibility about when we'll introduce that legislation," Hajdu told reporters before the Liberal caucus meeting Wednesday morning.

I really don't want to have to use back-to-work legislation, but this is a really busy time of year … and our economy needs Canada Post to be able to function in a smooth way. - Patty Hadju, federal labour minister

The government has also reappointed Morton Mitchnick as a special mediator in the labour battle and Hajdu said she'll let him take the time he needs.

"We've given notice to the House, we are extremely serious, [but] I really don't want to have to use back-to-work legislation," said Hajdu. "But having said that, this is a really busy time of year, people are relying on Canada Post to deliver packages, small and medium-size businesses are relying on Canada Post to have a profitable season, and our economy needs Canada Post to be able to function in a smooth way."

Canada Post is dealing with a fifth week of rotating strikes by thousands of unionized workers as both sides remain apart in contract negotiations.

Hajdu said the parties have already had a long time to work out a deal but she expects them to work hard over the next couple of days to reach an agreement.

Prime Minister Justin Trudeau addresses possible back-to-work legislation during question period.

PM Justin Trudeau says back-to-work legislation introduced yesterday will be used if the two sides in the Canada Post dispute can't come to an agreement. 2:28

The Canadian Union of Postal Workers on Monday turned down an offer for a holiday cooling-off period and a possible $1,000 bonus for each of its 50,000 members, saying it would only mean postal employees continuing to work under the same conditions the union is trying to have changed.

When asked if she worries about potential criticism from New Democrats for ending the strikes with a law, Hajdu said she has to do what's right for the country.

What's changed since the last labour disruption?

The Canada Post of today that finds itself struggling through rotating strikes is a very different organization from the postal service that last saw labour disruptions.

Back in 2011, as the company faced a labour dispute that led to its first loss in 17 years, then-CEO Deepak Chopra unveiled a plan to restructure the centuries-old institution to adapt to major structural changes brought on by the internet, including both a plunge in letter mail and a rise in packages.

"Starting in 2007, letter volumes started to collapse like a stone," said Ian Lee, an associate professor at Carleton University's Sprott School of Business in Ottawa, who has studied the Crown corporation.

"That was their bread and butter, their core business, and their most profitable. Vastly, by far their most profitable product was letter mail. They charged lots of money, and it cost very little to deliver it."

Striking Canada Post workers keep their hands warm as they picket at a Toronto sorting facility Nov. 13. A mediator has been appointed by the federal labour minister to settle the dispute. (Frank Gunn/Canadian Press)

By 2011, the Canada Post Group of Companies, which includes subsidiary Purolator Holdings Ltd., and others, was handling about 10 billion pieces of mail a year for a 1.8-billion drop from 2007.

Last year, total volume came in at 8.4 billion as the service has sustained a steady drop in its core business of transaction mail made of up letters, bills, statements, invoices and other paperwork that's now gone digital.

In response, the company switched emphasis to its parcel service, which for years had stayed at a fairly stable level.

But the transition hasn't been easy, said Lee, since unlike letter mail, parcel services have stiff competition from major international players like UPS and Fed Ex.

"People say, OK, well great, you lost one product line, you get another product line. It's not that simple … this is a very competitive space; there is no monopoly."

Still, a rapid rise in overall parcels being sent out to consumers has helped Canada Post record significant gains in the space.

Last year, parcel revenue came in at $2.1 billion, or about 33 per cent of Canada Post revenue, up from about $1.3 billion or 21 per cent of revenue in 2011.

Parcel volume has climbed from about 143 million packages in 2011 to 242 million last year for an almost 70 per cent increase.

In a 2016 annual report, Canada Post said it delivered nearly two-thirds of online orders by Canadians.

Canada Post, which for over 200 years was a protected monopoly of the state, is dying before our eyes, but the culture hasn't caught up. - Ian Lee, business prof, Carleton University

Lee said the service has been competitive, offering somewhat cheaper rates than private operators, but it's been saddled with labour costs, a large pension obligation, and a culture slow to change.

"Canada Post, which for over 200 years was a protected monopoly of the state, is dying before our eyes, but the culture hasn't caught up," he said.

Idle Canada Post trucks sit in the parking lot of the Saint-Laurent sorting facility in Montreal, on Nov. 15. (Ryan Remiorz/Canadian Press)

Pivoting has been hampered by difficult labour relations, pension obligations, as well as the structure of the service itself, said Malcolm Bird, associate professor of political science at the University of Winnipeg.

"They've got difficult labour relations, political interference in their operations, they've got to deliver mail to everywhere regardless of the cost, so there may be a few little advantages, but I suspect they would be far outweighed by their public service role."

Universal service costs more

A government discussion paper noted that labour costs are about 41 per cent higher than comparable businesses in the private sector.

Canada Post has to deliver to every address in Canada, but the number of addresses are increasing while each customer is using the service less. Parcel deliveries is a way to offset some of its costly obligations, said Bird.

"Canada Post, in raw political terms, it provides mail and package delivery services to rural and small town Canada, and the North, places where private companies provide limited service, if at all."

A striking Canada Post worker walks the picket line in front of the Saint-Laurent facility, on Nov. 15. Companies have been using the strikes to encourage customers to switch to online billing. (Ryan Remiorz/Canadian Press)

The requirements of delivery are what pushed the service into the community mailbox program and away from door-to-door delivery, a move that was expected to save about $400 million a year before the Trudeau government shelved the plan.

Despite steady declines of between four and eight per cent per year, letter mail still provides the bulk of Canada Post's revenues. Last year, transactional mail pulled in $2.9 billion to make up 45 per cent of revenue, down from $3.2 billion or 54 per cent in 2011. Advertising, or direct marketing mail, makes up the other main segment for the service at $1.1 billion in revenue last year.

The strike threatens its core business further, since companies have been using it to encourage more people to switch to digital, said Bird.

"Every single company that still provides paper letters, paper bills to people, is trying to use these rotating strikes to make even more people go on to electronic bills and get rid of paper."