A Conservative bill ordering 48,000 Canada Post employees back to work cleared the House of Commons on Saturday night after a marathon debate and several failed opposition efforts to win changes.

The House gave third reading to the bill shortly after 8 p.m. by a vote of 158-113 and then adjourned for summer.

The bill, which imposes a four-year contract and certain wage increases on the workers, now goes to the Senate, which has been called to sit at 11 a.m. ET on Sunday.

The back-to-work order would go into force 24 hours after receiving royal assent, Labour Minister Lisa Raitt told MPs.

While opposition members expressed fear for the rights of organized workers, Prime Minister Stephen Harper called the three days of round-the-clock debate over the bill "a completely unnecessary delay."

But Harper said he was pleased that "soon Canadians will again have access to their postal service, particularly small businesses and charities."

Third reading came at the end of a 58-hour filibuster, during which the opposition tried to either hold up or modify what it called a "draconian" bill — and after talks between Canada Post and the Canadian Union of Postal Workers collapsed again.

The Crown corporation locked out the employees on June 14, after the union conducted 12 days of rotating strikes.

Workers face binding arbitration

The back-to-work bill, introduced last Monday also imposes a form of binding arbitration in which each side would table its final offer and the arbitrator would pick one or the other. This provision and the imposed wage increases provoked the most debate.

Late Saturday afternoon, the House gave second reading to the bill, which then moved into committee-of-the-whole, the stage where the Opposition NDP and Liberals had hoped to propose changes.

At the opening of the committee debate, Raitt told MPs the postal dispute was expected to cause a "measurable" impact on the Canadian economy, with losses of between $9 million and $31 million a week.

"The parties in the dispute have tried again and again and again … and indeed there is no agreement in sight," she said.

But MP Thomas Mulcair, the deputy leader of the NDP, accused the Conservatives of rolling back the collective bargaining rights of workers.

"It's an indication of what's to come for other public service workers who are unionized," Mulcair said. "But it's also a signal from the Conservatives to all employers — in a union setting or otherwise — that it's an open bar. They can start going after the acquired rights of their workers."

As MPs voted on individual sections of the bill at the committee stage, it became clear the Conservatives weren't going to accept any changes.

One amendment sought by the NDP would have removed clauses forcing the two sides into final-offer selection by an arbitrator to end the dispute.

Another would have removed the salary provision of the bill, which the NDP said proposes a wage increase lower than what Canada Post had wanted to offer the union.

The Liberals favoured similar changes to end the "stubborn ideological debate" between the government and Opposition on the issue.

"The sterile and hopelessly polarized debate between left and right cannot go on forever," Bob Rae, the Liberal interim leader, said in a statement. "It's time for parliamentarians to put an end to this shambolic debate and find a solution to the impasse."

The New Democrats began the filibuster Thursday evening as MPs were scheduled to start their summer break. The non-stop stall continued all day Friday, with a setback for the NDP as Conservatives and Liberals joined to defeat a procedural motion.

Record for non-stop debate

The NDP had introduced a "hoist" motion to put off second reading for six months but failed to win approval after the Liberals joined the governing Conservatives to defeat it by a vote of 160 to 74.

MPs have set a record for non-stop debate on back-to-work legislation. The Conservative government says the old record of 27.5 hours was set in 1989.

Talks between Canada Post and the union collapsed late Wednesday, with pension issues at the heart of the stalemate.

Canada Post said there were discussions on Saturday morning, but they broke off and the two sides were still "far apart."

CUPW national president Denis Lemelin, who was seen mid-Saturday leaving Parliament Hill with other union officials, would not confirm whether talks had resumed.

With files from The Canadian Press