OTTAWA -- Mail service will resume all across the country at noon Tuesday after the Senate passed legislation ordering an end to five weeks of rotating strikes by postal workers.

Royal assent was granted late Monday shortly after senators approved Bill C-89 by a vote of 53-25. Four senators abstained.

The government had deemed passage of the bill to be urgent due to the economic impact of continued mail disruptions during the busy holiday season. It rushed the bill through the House of Commons last week.

But senators, after holding a special sitting Saturday to debate the bill, insisted on taking a little more time to reflect on the constitutionality of stripping postal workers of their right to strike.

They held another special sitting Monday and only put the bill to a vote after more than five hours of additional debate.

"I thought the extra time we took was valuable and was a demonstration of how the Senate should be reviewing government bills," said Sen. Yuen Pau Woo, leader of the independent senators' group.

Sen. Peter Harder, the government's representative in the Senate, urged senators earlier Monday not to delay any further.

"I'm gratified that after two days of intense debate the Senate did what, in my view, is the right thing and passed this legislation," he said after the vote.

The Canadian Union of Postal Workers issue a statement declaring that it is "exploring all options to fight the back-to-work legislation."

"Postal workers are rightly dismayed and outraged," said CUPW national president Mike Palecek. "This law violates our right to free collective bargaining under the Charter of Rights and Freedoms."

Some senators -- independents, Liberal independents and even some Conservatives -- agreed with that assessment and voted against the bill.

But the majority either disagreed or concluded that it's up to the courts, not senators, to rule on constitutionality.

An amendment by independent Sen. Murray Sinclair, who proposed delaying implementation of the back-to-work order for at least seven days after royal assent, was rejected.

Earlier Monday, Labour Minister Patti Hajdu said that the special mediator had concluded his work and the two sides were no longer negotiating.

Negotiations have been underway for nearly a year, but the dispute escalated more recently when CUPW members launched rotating strikes Oct. 22.

Those walkouts have led to backlogs of mail and parcel deliveries at the Crown corporation's main sorting plants in Vancouver, Toronto and Montreal.

Picket lines were up Monday in parts of British Columbia, including Vancouver, Richmond and Surrey, and in parts of Ontario, including Hamilton, Ajax, North York, Pickering and London. Workers also walked off the job in Halifax and Dartmouth, N.S.

During debate, Harder told senators that failure to speedily pass Bill C-89 would have severe consequences for those who rely on stable mail delivery service, including the elderly, residents in rural and remote areas and, most especially, retailers who use Canada Post to deliver online purchases.

"It is the government's strong view that if it does not act now to protect the public interest, it will have acted too late," he told the Senate, arguing that postal disruptions are "not merely inconvenient."

"The strikes come at a critical period for retailers," Harder said.

"Unlike other kinds of e-commerce transactions ... lost holiday sales are unlikely to be deferred to a later date. They represent real and actual lost business for these companies."

Canada Post said Monday that the backlog of mail and parcels is "severe" and expected to "worsen significantly" once online orders from Black Friday and Cyber Monday sales are processed.

In a statement, the post office said it is experiencing delivery delays across the country and that's expected to continue throughout the holiday season and into January.

The union wants better pay and job security, guaranteed hours for its 8,000 rural and suburban carriers, and equality for those workers with the corporation's 42,000 urban employees.

CUPW also wants Canada Post to adopt rules that it says would cut down on workplace injuries -- an issue the union has said is now at a "crisis" level.

Under the new legislation, the union said postal workers will be forced to go back to work under the old collective agreement, which it asserted would result in at least 315 disabling injuries and thousands of hours of forced, unpaid overtime.

The previous Conservative government forced an end to a lockout of postal workers during a 2011 dispute by enacting back-to-work legislation, which was later declared by a court to be unconstitutional.

But the Liberal government argues Bill C-89 is different, in that it does not impose immediate outcomes affecting postal contracts.

Whereas the 2011 bill imposed a settlement that favoured Canada Post, the current legislation would give a mediator-arbitrator appointed by the government 90 days to try and reach contract settlements. Failing that, a settlement could be imposed either through a decision from the arbitrator or by choosing from one of the final proposals put forward by Canada Post or CUPW.

In drafting the bill, Harder said the government has taken into account court rulings and is confident that its limitations on the right to strike would be upheld as a reasonably justifiable infringement of charter rights in a free and democratic society.

Independent Sen. Marc Gold, a former constitutional law professor, said he's inclined to agree with the government.

But another independent, Sen. Andre Pratte, said the bill makes "a fair, negotiated agreement impossible by depriving workers of the lone source of their bargaining power, their right to strike."

"Because the right to strike is a fundamental right ... I am convinced that more time should be allowed for negotiations to come to a fruitful conclusions," he said.

While not all Conservative senators supported the bill, several of their colleagues slammed the Liberal government for failing to put an end to the strikes sooner.

"This government was so concerned with appearances, not wanting to look like previous governments, wanting instead "to wag their finger and lift their chin in righteous indignation, that they sat on their hands until it was almost too late. And it still might be too late," Conservative Sen. Leo Housakos told the upper house.

Fellow Conservative Sen. Don Plett said "the government sat on its hands until the 11th hour and then in a panicked rush suddenly decided something needed to be done."