Under threat of back-to-work legislation that could pass through the Senate by late Monday, negotiators remained at the bargaining table Sunday in a last-ditch effort to bring an unforced end to rotating walkouts at Canada Post.

Some Canadians, meanwhile, were receiving packages delivered through the Crown corporation, but at a much slower pace than normal for this time of year.

Crown corporation spokesman Jon Hamilton said work restrictions imposed by the Canadian Union of Postal Workers, including a ban on overtime, meant only about 30,000 parcels would likely be delivered to Canadians over the weekend.

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Opinion: Even if back to work, Canada Post is still plagued by deeper issues

Parcel delivery volumes are normally in the range of 500,000 packages on late November weekends, said Mr. Hamilton.

“Weekend deliveries occur during the holidays to keep pace and balance the workload through the week,” he said.

“In 2017 we delivered 3.6 million parcels on holiday weekends.”

The Senate was set to resume special debate Monday afternoon (2 p.m. ET) on back-to-work legislation that was introduced by the Trudeau Liberals and passed Friday in the House of Commons.

A final vote on the bill is possible by early evening with royal assent soon afterward, barring any proposed amendments that, if passed, could see the legislation returned to the Commons, a Senate official said.

Postal workers have been holding rotating strikes across the country since Oct. 22, creating substantial backlogs at Canada Post’s main sorting plants in Vancouver, Toronto and Montreal.

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Picket lines were up on Sunday in Sault Ste. Marie, Ont., as well as in a few areas of British Columbia, with the union vowing to continue the walkouts Monday.

CUPW national president Mike Palecek warned that “all options are on the table” as the union decides how to fight the back-to-work legislation once it becomes law, which the union said violates the rights of postal employees.

“Postal workers will not accept another violation of our right to free collective bargaining,” Palecek said in a statement on the union’s website.

“It’s not just a matter of our Charter rights. This bill legislates continued injuries, unpaid work, gender inequality and general dishonesty and disrespect.”

The former Conservative government forced an end to a lockout of postal workers during a dispute in 2011 by enacting back-to-work legislation.

That bill was later declared by a court to be unconstitutional.

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But the Liberal government’s legislation, known as Bill C-89, is “different” in that it does not impose immediate outcomes affecting postal contracts, Labour Minister Patty Hajdu said shortly after the legislation was tabled in the Commons.

After hours of debate during a special Saturday session, the Senate voted to give its members a day to reflect on witness testimony about the bill, adjourning their discussions until Monday afternoon.

The legislation was sent to the Senate early Saturday after the Liberals pushed it through the House of Commons.

CUPW’s 50,000 members, in two groups, are demanding better pay for rural and suburban carriers, as well as greater job security and minimum guaranteed hours.

The union also wants Canada Post to adopt rules that would cut down on workplace injuries, an issue Palacek said has evolved into a “crisis” in recent years.