Conservative senators say they wanted to push Canada Post back-to-work legislation through on Sunday but are pointing the finger at independent senators for delaying the third and final reading until Monday.

The House of Commons introduced the bill earlier this week and pushed it through in quick fashion, then asked the Senate to do the same.

Conservative Senator Leo Housakos said his caucus had signalled to the Independent Senators Group (ISG) they were willing to sit on Sunday to pass Bill C-89 as soon as possible.

"We offered our full cooperation to get it read, tabled and passed by [Sunday] afternoon," Housakos said in an interview with CBC News.

After nearly eight hours of proceedings in a rare weekend sitting on Saturday, the Senate agreed to hold the third and final reading of the bill on Monday afternoon.

But Housakos said a majority of the upper chamber were willing to sit on Sunday until a few members of the ISG blocked the motion.

"They had members in their caucus who were not onside and were not going to grant leave [to immediately proceed with the final reading]."

Members of the Canadian Union of Postal Workers (CUPW) have held rotating walkouts for more than a month, causing backlogs of unsorted mail and packages at postal depots.

The controversial back-to-work bill, if passed, would go into effect at noon ET on the day following royal assent.

Watch: Patty Hajdu explains the need for back-to-work legislation

Employment Minister Patty Hajdu begins debate in the House of Commons on an act that would enforce the resumption and continuation of postal services. 1:55

When Senator Peter Harder, the government's representative in the Senate, asked for unanimous consent to proceed to the third reading of the bill, a few senators voiced their opposition.

Senator Yuen Pau Woo, facilitator of the independent group, said he opposed moving the bill through too quickly in order weigh both sides of the postal debate.

"We heard contradictory testimony from witnesses, which makes it difficult for us to get an accurate picture of what is going on. I am happy to have a day for reflection before we resume debate on Monday," Woo said in an email.

"We are acting with haste, but we are not acting hastily."

Holidays fast approaching

On Saturday senators heard from the interim president of Canada Post and the head of the union.

"I didn't want to be here discussing back-to-work legislation," Jessica McDonald of Canada Post admitted.

"Despite extensive efforts … we have not been able to find the common ground needed."

Watch: Canada Post strike in Moncton

Raw footage from Moncton of the ongoing Canada Post strike. Canada Post is in its fifth week of rotating strikes by thousands of unionized workers, with no sign yet of a breakthrough in contract negotiations. 0:30

CUPW President Mike Palecek shared multiple stories of workers who had been injured on the job, or who work such extensive overtime they barely see their families.

For his part, Housakos stressed his support for the bill because the holidays are approaching and Canadians would be relying on postal services to deliver packages.

"This is going to have a devastating effect on the commercial industry in Canada that depends so heavily on Christmas sales," he said.

Constitutional concerns

Union leaders have repeatedly argued the bill is in violation of their rights to collective bargaining.

In 2011 the then-Conservative government passed back-to-work legislation demanding an end to a Canada Post lockout and rotating strikes by postal workers.

But that legislation was overturned by the courts in 2015, after a ruling that by removing workers' right to strike, the bill violated their right to freedom of association and expression.​

Canada Post workers walk the picket line as a rotating strike continues in Halifax on Tuesday, Nov. 13. Rotating strikes continue across Canada this weekend but negotiatons are also going ahead. (Andrew Vaughan/Canadian Press)

The current Liberal government on the other hand believes they have crafted the bill in a way that does not violate charter rights, because it does not impose immediate outcomes affecting postal contracts.

Housakos said the current legislation could possibly be overturned but he reiterated that his primary concern is ensuring mail is being delivered.

"More important than that is making sure that the trucks are rolling, the mail is being delivered and the Canadian economy and Canadian public is being served."

CUPW has already vowed to fight the legislation in court, which Housakos said they have a right to do.

Meanwhile negotiators from both sides remained at the bargaining table Sunday in a last-ditch effort to bring an unforced end to rotating walkouts, but with little sign that a deal would be reached before the Senate returns for the final reading.

Senators are set to return for the third reading on Monday at 2 p.m. ET.

With files from the Canadian Press