Weeks of tension between the Liberal government and the Senate will come to a head on Friday when senators must decide whether to stand their ground on the physician-assisted dying bill.

The House of Commons on Thursday passed a government motion to accept most of the seven amendments in Bill C-14 made by senators this week – but rejected a key proposal to include patients who are not at the end of life. That proposal, which would have opened up medically assisted dying to people with mental or non-terminal conditions, has been a major point of contention between the government and the Senate.

The bill is now back in the hands of senators, who will decide whether to change the legislation, pass it or reject it – the latter resulting in a back-and-forth scenario between the two Houses as summer break looms. And the ensuing debate could force the government to extend the sitting of this Parliament past its scheduled close next week.

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The legislation is the result of a 2015 Supreme Court decision, which struck down the ban on assisted dying in Canada and gave Parliament until June 6 to come up with a new law. The Liberals missed that deadline, which means there is no federal law dictating medical assistance in dying. It is now up to provincial regulatory bodies to govern the procedure – although an Ontario court judge recently ruled a court's permission is necessary until a law is in place. The Canadian Medical Association is also pushing for federal legislation.

Independent Liberal Senator Serge Joyal is set to introduce yet another amendment to the bill dealing with the requirement that a patient's natural death be "reasonably foreseeable" – a criteria many have argued is unconstitutional and condemns Canadians who are not terminally ill to years of suffering.

"We will see how the debate unfolds," Mr. Joyal said Thursday evening. "It's difficult to predict."

Mr. Joyal has also suggested the end-of-life section of the bill be sent to the Supreme Court for evaluation – although the government has already shut that possibility down.

Newly appointed independent Senator Ratna Omidvar says she, along with many of her colleagues in a less-partisan but unelected body, is torn about going up against the elected Commons for a second round.

"How far do we go?" she asked. "I'm not quite sure at this point."

"I'm very mindful of the fact that I'm not … an elected parliamentarian."

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Conservative Senate Leader Claude Carignan said the updated bill is an improvement from the original – and he doesn't expect widespread support for Mr. Joyal's amendment.

"My feeling is that we have a good result now. We have a better bill," he said Thursday, although he added he still worries about the legislation's constitutionality.

Senate Liberal Leader James Cowan says he, along with many of his colleagues, cannot support a bill that limits assisted dying only to those at the end of life.

"I think we should broaden it. Otherwise, I don't think the bill will pass constitutional muster. I think it will be struck down," he said.

After an expedited debate in the House on Thursday, the government motion to amend the bill passed in a vote of 190 to 108, supported by all but three Liberals and almost two dozen Conservative MPs.

The amendments accepted by the Commons include presenting palliative-care options to patients, reporting requirements for the health minister, completing independent reviews of topics such as advance requests within two years, and two minor technical changes.

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The government also adopted in part a proposal that beneficiaries shouldn't be allowed to sign on behalf of patients – but removed the ban that said they can't help the person end their own life, arguing that wouldn't allow family members or friends to assist.

But the Liberals outright rejected the Senate amendment that removes the criteria that a patient's natural death be "reasonably foreseeable" in order to qualify for medical assistance in dying.

"I am confident that Bill C-14 as originally drafted and presented in this place is constitutional," Justice Minister Jody Wilson-Raybould told the Commons.

For weeks, the government has been arguing that removing end-of-life criteria would put vulnerable Canadians with mental-health issues or disabilities at risk.

"We respect the Senate's perspective and highlighted that there are a number of things they've proposed that we feel are improvements to the medical-assistance-in-dying bill, which we gladly accept," Prime Minister Justin Trudeau said at a press conference in Burnaby, B.C., on Thursday.

"But we do not want to affect the fundamental balance that we achieved in this piece of legislation between protecting vulnerable Canadians and allowing for rights and freedoms."

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A last-ditch attempt by NDP MP Murray Rankin to return the Senate's amendment back into the bill failed. Liberal MP Rob Oliphant, who originally voted against the bill, said he believes the legislation is flawed and will be challenged by the courts. But he supported the amended version of the bill on Thursday.

"It is now apparent to me that having legislation in place will at least save vulnerable Canadians from the costly and inhumane tribulation involved in having to appear before a judge to access their right to medical assistance in dying," he said in a statement.