Care Not Killing is warning against changing UK laws on euthanasia following the death of Olympic gold medallist Marieke Vervoort.
The coalition, which is opposed to the legalisation of assisted suicide, said it was "extremely sad" that the Belgian paralympian had chosen to end her life.
The 40-year-old won gold and silver at the London 2012 Olympics, and another silver at the Rio 2016 games.
She suffered from an incurable degenerative muscle disease that left her relying on pain killers. In a BBC interview in 2016, she said that the pain sometimes caused her to "scream" and that she also suffered from epileptic attacks.
In 2008, she signed papers in her native Belgium, where euthanasia is legal, giving doctors permission to assist in her death in the future.
Dr Gordon Macdonald, chief executive of Care Not Killing, said it was important that the status quo be retained in the UK.
"It is extremely sad news that Ms Vervoort has chosen to end her life this way," he said.
"But her death highlights how the right to die has become a duty to die in both Belgium and their near neighbours in the Netherlands.
"In these countries, laws which were only ever supposed to apply to mentally competent terminally ill adults have been extended and safeguards removed.
"Euthanasia laws in Belgium and the Netherlands now include those who are not terminally ill, disabled people, non-mentally competent adults, those with mental health problems, couples and even children."
Euthanasia was legalised in Belgium in 2002 for adults with conditions causing unbearable suffering and with no prospect of improvement. In 2014, the law was extended to allow euthanasia for children.
Over the years, the application of euthanasia laws in Belgium has expanded to include people with mental conditions. In the case of 64-year-old Godelieva de Troyer, she was physically healthy but euthanised after struggling for many years with mental health problems. The decision to euthanise her is being challenged by her son in the European Court of Human Rights.
The British Medical Association, Royal College of GPs, British Geriatric Society and the Association for Palliative Medicine are all opposed to changing UK law on assisted suicide.
The Samaritans runs a free 24/7 helpline for anyone struggling with suicidal thoughts. Call 116 123 for help.
