Senators voted in favour of the Liberal government's legislation to force Canada Post employees back to work — a move that was quickly given royal assent.

The vote on Monday evening, passed by a margin of 53 to 25 with four senators abstaining, ends a series of rotating strikes at Canada Post as the walkouts enter their sixth week. Canada Post workers will have to be back on the job as early as 12:00 p.m. ET Tuesday.

"The Senate performed the role that it's supposed to, which is that of providing review and sober second thought," said Peter Harder, the government representative in the Senate. "We studied the issue, debated it and ultimately, we decided."

Negotiations have been underway for nearly a year, but the dispute escalated more recently when members of the Canadian Union of Postal Workers 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.

"Postal workers are rightly dismayed and outraged," CUPW national president Mike Palecek said in a statement. He added that postal workers will "continue to defend our right to negotiate a settlement."

"If the Trudeau government thought that passing this legislation would end the dispute, they've made a mistake."

'Last resort'

Royal assent was signified in the Senate chamber shortly after 9 p.m. ET by Gov. Gen. Julie Payette's deputy, Assunta Di Lorenzo.

"The work stoppage at Canada Post has had significant negative impacts on Canadians, charities, businesses of all sizes, international commerce, Canada Post, its workers and their families," Labour Minister Patty Hajdu said in a statement.

"Back-to-work legislation is a last resort and not something we take lightly. However, having exhausted all other options, it is necessary to protect the public interest and avoid further harm to the Canadian economy."

Conservative Sen. Leo Housakos welcomed the outcome of the vote.

"I am relieved," he said. "I am happy that with a little bit of prodding the Senate took the right decision on behalf of the Canadian economy and the Canadian people right on the eve of Christmas."

Bill C-89 was debated in the upper chamber on Saturday after the Liberal government fast-tracked the legislation through the House of Commons.

But despite an initial plan to continue debate — and possibly hold a vote — on Sunday, senators chose instead to give themselves an extra day to digest hours of witness testimony on the labour dispute.

An attempt to push the final vote on the bill back seven days by Sen. Murray Sinclair in order to find Canada Post and the union representing workers time to sort out some health and safety issues failed to pass a vote.

Bill C-89 would impose heavy fines

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 said would cut down on workplace injuries — an issue the union has said is now at a "crisis" level.

The union's national president has called the back-to-work bill a slap in the faces of Canada Post employees and accused Prime Minister Justin Trudeau of turning his back on postal workers.

Canada Post workers in Edmonton remained on strike Monday as negotiations with the Crown Corporation stalled. (Emilio Avalos/CBC)

The former 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.

Arbitration

But the Liberal government's bill is "different," Labour Minister Patty Hajdu said shortly after the legislation was tabled in the Commons, in that it does not impose immediate outcomes affecting postal contracts.

The 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.

Bill C-89 imposes fines of between $1,000 and $50,000 per day on anyone found in contravention of the Act, and up to $100,000 per day against Canada Post or the union if they are found guilty of violating its terms.

Canada Post said it expected to make about 30,000 deliveries of parcels to Canadians over the past two days — a far cry from the 500,000 deliveries that a company spokesman said was normal for a late-November weekend.

"Weekend deliveries occur during the holidays to keep pace and balance the workload through the week," said Canada Post spokesperson Jon Hamilton.

"In 2017, we delivered 3.6 million parcels on holiday weekends."