The Liberal government is set to introduce its much-anticipated physician-assisted-dying law on Thursday, a bill that will exclude those who only experience mental suffering, such as people with psychiatric conditions, according to a source familiar with the legislation.

The bill also won't allow for advance consent, a request to end one's life in the future, for those suffering with debilitating conditions such as dementia. In addition, there will be no exceptions for "mature minors" who have not yet reached 18 but wish to end their own lives.

Those three issues, however, will be alluded to in the legislation for further study, according to the source, who is not authorized to speak publicly about the bill.

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The law comes in response to a February, 2015, Supreme Court decision that unanimously struck down the Criminal Code ban on assisted dying, and gave Parliament a year to come up with a new law that applies to competent adults with a grievous and irremediable medical condition that causes enduring suffering and who clearly consents to ending his or her own life.

In February this year, the court granted the Liberal government a four-month extension until June 6 to draft a new law.

The government's bill is set to take a much narrower approach than recommended by a joint parliamentary committee it struck to study the issue over two months this winter.

After hearing from 61 witnesses, the committee issued a report that recommended patients suffering from terminal and non-terminal grievous and irremediable illnesses who experience enduring suffering, either physical and/or psychological, should be eligible for doctor-assisted dying. It also said those with psychiatric conditions should not be excluded from eligibility based solely on that fact.

The committee also said advance consent should be written into the bill and that legislation for competent mature minors should come into force no later than three years after the first law is passed.

The driving voices behind the Supreme Court challenge say the expected legislation doesn't go far enough to protect those who are suffering.

"I'm disheartened," Lee Carter, one of the plaintiffs in the Supreme Court case said, whose mother, Kay, suffered from spinal stenosis, a degenerative condition that left her in a wheelchair and in chronic pain. Kay Carter travelled to Switzerland in 2010 to end her life.

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Ms. Carter said she's particularly upset about advance consent being excluded.

"Our family has spent more than five years on this issue, and the parliamentary committee advocated for the advanced request," she said.

"The Liberal government just doesn't have the jam, or the nerve, or the pluck, or the spine to honour them."

Josh Paterson, lawyer and executive director of the British Columbia Civil Liberties Association, another plaintiff in the case, said he anticipates more court challenges if the legislation isn't broadened to include the committee's recommendations, including mental illness.

"We see it as deeply, deeply problematic that on one of the first pieces of legislation, a high-profile piece of legislation in this government that speaks very eloquently about respecting the Charter, that they may be about to violate the rights of people who are suffering deeply," he said.

Justice Minister Jody Wilson-Raybould said Tuesday the government has been working "thoughtfully" on the legislation, but wouldn't go into detail about its contents.

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"We will bring forward our government response that seeks to provide that balance between personal autonomy, recognizing the conscience rights of medical practitioners and ensure that we do as much as we can to protect the vulnerable," she told reporters.

Conservative MP Michael Cooper, one of the committee's vice-chairs who argued for a limited scope on assisted dying, said if the anticipated bill excludes minors, advanced directives and people with mental illnesses, "then that is a step in the right direction."

But he questioned how the Liberal government expects to debate, study and pass its law by June 6, especially in the Senate, where Liberals are no longer part of the government's caucus.

"It seems to be a very, very compressed timeline to successfully get passed through both Houses what is a very complex and sensitive piece of legislation," he said. "So, I'd be interested to see how the government plans to do that."