Removing the age limit on euthanasia in Belgium will be a betrayal of those in society who are the most vulnerable, the Parliamentary Assembly of the Council of Europe has warned.
Belgium first legalised euthanasia for adults in 2002, and is now considering removing the age limit to extend it to children with terminal illnesses who are in extreme pain.
Members of the assembly expressed their opposition to this plan in a written declaration last week.
The declaration from the Council of Europe references a 2012 Parliamentary opinion on the matter, which states that: "Euthanasia, in the sense of the intentional killing by act or omission of a dependent human being for his or her alleged benefit, must always be prohibited."
It also quotes an earlier recommendation from the Parliamentary Recommendation in 1999 encouraging the member States of the Council of Europe "to respect and protect the dignity of terminally ill or dying persons in all respects by upholding the prohibition against intentionally taking the life of terminally ill or dying persons".
The Council of Europe went further in last week's declaration to specifically oppose allowing euthanasia for children, arguing that the proposed Belgian law "mistakenly assumes that children are able to give appropriate informed consent to euthanasia and that they can understand the grave meaning and complex consequences associated with such a decision".
In condemning all forms of euthanasia, the declaration said that the idea of killing for the sake of mercy "promotes the unacceptable belief that a life can be unworthy of life which challenges the very basis of civilised society".
The Council of Europe's Parliamentary Assembly, which is made up of elected and unelected representatives from all across Council of Europe's 47 member countries, has 35 British MPs and Peers as part of the assembly.
British signatories to the declaration include Sir Edward Leigh and Sir Alan Meale.
Advocacy group Christian Concern has endorsed the declaration and is asking people to email British members of the assembly who have not signed it.
The Child Euthanasia Bill was already passed in the Belgian senate by 50 votes to 17, and is expected to face a vote in the lower house next Thursday.
Philippe Mahoux, leader of the Socialist group in the Belgian Senate and sponsor of the bill, was quoted on BBC News describing the bill's proposals as "the ultimate gesture of humanity".
"The scandal is that children will die from disease," he says. "The scandal is not to try and avoid the pain of the children in that situation."
Christian Democrat Els Van Hoof, a Senator opposing the bill, argued that it is based on a dangerous misconception of self-determination. Her lobbying successfully limited the bill to children with terminal illness suffering unbearable physical pain.
Quoted on BBC news, she said: "In the beginning they presented a law that included mentally ill children."
But talking of the danger of a slippery slope, she noted that "during the debate, supporters of euthanasia talked about children with anorexia, children who are tired of life - so how far does it go?
"It is strange that minors are considered legally incompetent in key areas, such as getting married, but might (be able) to decide to die," Catholic Archbishop Andre-Joseph Leonard said in his testimony to the Belgian Senate.
A petition to oppose the change in the legislation on the website CitizenGo.org has amassed more than 56,000 signatures.
In an appeal to the President of the Belgium Commission of Justice and President of the Social Affairs Committee, the petition says: "Regardless of disability, life should be valued.
"To pass legislation that allows termination of life without reason is unacceptable and immoral."