Labour Minister Lisa Raitt said "an erosion" at the bargaining table between Canada Post and its union forced the government to serve notice it will table back-to-work legislation if the two sides can't reach a deal.

Raitt had previously said she preferred to see Canada Post and the Canadian Union of Postal Workers come to a negotiated settlement.

But after Canada Post locked out its 48,000 urban postal workers late Tuesday, Raitt said the "drastic" move forced her to reassess the impact on the Canadian public and the economy.

"What it comes down to is we've got two parties, the union and Canada Post, that have been at the table for a very, very long period of time," Raitt told CTV's Power Play Wednesday evening. "What we've been seeing in the past last 11 days is just an erosion at the table."

Raitt added: "As you know…(the government has) a strong mandate from Canadians to have an economic recovery that works and to work on it, and this is an important piece of it as well. The harm to the third parties, especially the small businesses, is of great concern and we acted appropriately today."

On Tuesday, the government issued a similar warning to striking Air Canada staff.

Raitt told Power Play the company pension is one of the main sticking points for both Canada Post and the union, as well as Air Canada and its union, and there has been little movement by either side on the issue.

At the end of the day, Raitt said, the government respects the collective bargaining process, but it must also consider third parties that suffer from work stoppages.

"There's a point in time where the innocent third parties affected," Raitt said. "It's one thing to withhold your services to a company in order to make them hurt economically so that they come back to the table. It's quite another thing to withhold services from the Canadian public so that they cause an economic difficulty for the entire nation in order to get their way. And that's just not acceptable."

Raitt urged Canada Post and CUPW to use the next 48 hours to "get to the table and do a deal."

Opposition critics say the government is going against traditional labour practices, where an agreement is eventually hashed out at the bargaining table.

And NDP MP Yvon Godin accused the postal service of "creating a crisis" by locking out workers, forcing the government to act.

Responding to reports that Raitt would use legislation to end the strike, union president Denis Lemelin said it was not a step that CUPW would agree with.

But he said the union's focus was on securing a meeting with Canada Post CEO Deepak Chopra.

Lemelin said Chopra should reinstate the prior contract agreement, which could be used while the two sides continue negotiating.

Earlier Wednesday, Lemelin said Canada Post's decision to shut down its urban operations across the country was "totally irresponsible."

Canada Post spokesperson Jon Hamilton said the lockout was not something the corporation wanted to do.

"While we'd hoped to avoid a disruption to service to Canadians, we feel we can't continue to let this drag on," Hamilton told The Canadian Press in an interview.

"It's having a huge impact on the business, it's having a huge impact on our customers and our employees and the time is now to get a deal with the union."

A statement issued by Canada Post late Tuesday said "a lockout is the best way to bring a timely resolution to this impasse and force the union to seriously consider the proposals that address the declining mail volumes and the $3.2-billion pension deficit."

Canada Post maintains that it has been forced to stop its urban mail services in the face of the rotating strikes that have raged for nearly two weeks, costing the corporation an estimated $100 million in revenue.

With files from The Associated Press and The Canadian Press