(OSV News) -- Cardinal Vincent Nichols of Westminster has joined leading Catholic politicians and pro-life groups in calling on U.K. Catholics to take immediate and urgent action to oppose an assisted suicide bill that he says will strike "fear and trepidation" in vulnerable people.

Labour Member of Parliament Kim Leadbeater is proposing a bill that would give terminally ill people in England and Wales the right to end their life. It will be introduced to the House of Commons Oct. 16, with a vote to take place Nov. 29.

The issue was last voted on in 2015, when MPs roundly rejected assisted suicide, with 118 votes for and 330 against.

In a pastoral letter to be read aloud in parishes in his London-based Diocese of Westminster Oct. 12-13, Cardinal Nichols, president of the Bishops' Conference of England and Wales, said that "this proposed change in the law may be a source of relief to some. But it will bring great fear and trepidation to many, especially those who have vulnerabilities and those living with disabilities."

Current U.K. law states that euthanasia and assisted suicide are illegal, with those found guilty facing up to 14 years in prison. While the contents of the new bill are as yet unknown, it is believed that it will offer terminally ill adults with six months or less to live the option of ending their lives with medical assistance.

Leadbeater said that the proposed bill will only apply to adults who are suffering from terminal illnesses. "I'm really clear. This is about people who are terminally ill", she told Sky News Oct. 3.

However, many expressed great concern when the British media reported that a group of 54 cross-party MPs are already calling for the assisted suicide bill to be applied to those who are "incurably suffering" as well as to those who are terminally ill.

Cardinal Nichols shared his own concerns about the reality of the "slippery slope" -- a movement toward increasingly widening interpretations of the law, based on evidence from places across the world where assisted suicide has been legalized.

"The evidence from every single country in which such a law has been passed is clear," he said. "That the circumstances in which the taking of a life is permitted are widened and widened, making assisted suicide and medical killing, or euthanasia, more and more available and accepted."

Cardinal Nichols, who called for improved palliative care and hospice provision, urged Catholics to not stay silent on the issue, but to play an active part through prayer and discussions with family, friends and colleagues.

He also called on the faithful write to their MPs to express their opposition to the assisted suicide law. "Be careful what you wish for," he warned. "The right to die can become a duty to die; being forgetful of God belittles our humanity."

Cardinal Nichols pointed out that questions raised by the assisted suicide legislation strike at the heart of "how we understand ourselves, our lives, our humanity," and underlined Catholic teaching on the human person. He said that "every human being is made in the image and likeness of God. That is the source of our dignity and it is unique to the human person. The suffering of a human being is not meaningless. It does not destroy that dignity."

Assisted suicide has become a major issue in the U.K. after popular journalist and television presenter Esther Rantzen, who has terminal cancer, called for a vote on assisted suicide earlier this year. Prime Minister Keir Starmer, who personally supports a change in the law, promised Rantzen that he would give MPs a free vote on the issue if he became prime minister, which happened when Labour won the general election July 4.

However, Catholic Lord David Alton, like Cardinal Nichols, warned Starmer that the "floodgates" will open, and vulnerable people will be at risk, if the law is passed in the same way as other jurisdictions.

"Before the U.K. Parliament opens the euthanasia floodgates," he said, "it should first dispassionately consider outcomes in jurisdictions that have ditched protection of the vulnerable with ineffective safeguards. MPs should put their energy into better palliative care."

One of the places Alton was referring to is the Netherlands, where euthanasia has been legal since 2002. Twenty-four confirmed cases of euthanasia have taken place where the individuals concerned were diagnosed with autism or having a learning disability.

In Canada, euthanasia and assisted suicide were legalized in 2016 on the condition that the death of applicants should be "reasonably foreseeable." In 2021, this condition was repealed. With a provision to exclude those with mental illness due to expire earlier this year, in February lawmakers delayed expanding euthanasia and assisted suicide on the grounds of mental health alone to March 2027.

Lord Alton instead called for "more hospice care at home and an ethos which upholds human dignity and the sanctity of life."

Cardinal Nichols also shared his worries "for all medical professionals," warning that their roles will change profoundly, which he described as "a slow change from a duty to care to a duty to kill."

Meanwhile, Bishop Mark Davies of Shrewsbury will also urge Catholics at Oct. 13 Masses to resist moves in Parliament to legalize assisted suicide.

In his letter, Bishop Davies predicts dire consequences if Parliament chooses a "dark and sinister path" toward a society in which the medical profession will be asked to assist in the killing of their patients.

"As we see populations ageing across western countries with a diminished number of younger people to support them, this is an especially dangerous moment for politicians to open the door to euthanasia: the medical killing of the sick, the disabled and the elderly," Bishop Davies wrote in a letter.