A man with Down's syndrome is suing an NHS trust over a hospital's decision to issue a do-not-resuscitate order giving his disability as one of the reasons.
The instruction not to attempt resuscitation in the event of a cardiac or respiratory arrest was issued without his family's knowledge.
Their lawyers describe the order as "blatant discrimination".
East Kent Hospitals University NHS Foundation Trust says it complied fully with guidance from professional bodies.
The family of the man, who can be identified only as AWA because of a court order, remained unaware of the do-not-resuscitate (DNR) decision until he had returned from hospital to his care home.
The DNR form, issued while he was in hospital in Margate a year ago, was listed as an indefinite decision, meaning it would cover the duration of his stay in hospital, with no provision for review.
The reasons given were "Down's syndrome, unable to swallow (Peg [percutaneous endoscopic gastrostomy] fed), bed bound, learning difficulties".
AWA, 51, has dementia and was having a special tube fitted to help him with feeding.
The form says there was no discussion with his next of kin because they were "unavailable", but the family say they visited him in hospital "virtually every day" - and a carer from his home sometimes attended too.
One of AWA's close relatives, who is pursuing the legal action on his behalf, said: "Until his dementia started three years ago, he had a really hectic social life. He loved parties, discos and going to church.
"He was looked after at home for as long as possible, but then we got him into a nice care home. His health deteriorated a bit - he had eating problems and couldn't swallow - so the decision was taken to have a Peg inserted so he could receive medication, foods and liquids.
"He was admitted to hospital for a fortnight. When he was discharged, one of the carers at his home was unpacking his bag and found the DNR form, to their horror.
"We weren't aware of the DNR until then. We were very angry and quite distressed, especially as he'd been re-admitted that day because he'd got pneumonia.
"Since November last year, he's been right as rain. He has a specially adapted chair, takes part in various activities and is conscious of everybody around him most of the time.
"He has a good way of life now, but somebody wasn't prepared to give him the time of day."
AWA and his family are represented by solicitor Merry Varney, from Leigh Day & Co.
She said: "This is definitely one of the most extreme cases we have seen of a DNR order being imposed on a patient without consent or consultation.
"To use Down's syndrome and learning difficulties as a reason to withhold lifesaving treatment is nothing short of blatant discrimination.
"If an individual was physically preventing a doctor from administering life-saving treatment to a disabled relative, it would undoubtedly be a matter for the police, yet we see doctors taking this decision without consent or consultation regularly."
Mark Goldring, chief executive of learning disability charity Mencap, said: "We are very disappointed to hear about this case, but unfortunately, we believe that DNR orders are frequently being placed on patients with a learning disability without the knowledge or agreement of families. This is against the law.
"All too often, decisions made by health professionals are based on discriminatory and incorrect assumptions about a patient's quality of life.
"People with a learning disability enjoy meaningful lives like anyone else. Yet... prejudice, ignorance and indifference, as well as failure to abide by disability discrimination laws, still feature in the treatment of many patients with a learning disability.
"Health professions need to understand their legal duties when treating people with a learning disability, and be held to account when their fail to do so."
Dr Neil Martin, medical director for East Kent Hospitals University NHS Foundation Trust, said: "The trust cannot comment on this individual case because it is subject to ongoing legal proceedings.
"East Kent Hospitals has put a great deal in place in recent years to meet the needs of vulnerable patients, including practical steps to improve communication with people with learning disabilities and their carers.
"It has a clear and robust policy in place on 'Do Not Attempt Cardio-pulmonary Resuscitation', which complies fully with national guidance from the professional bodies."
Ms Varney is leading a separate legal case to try to make the Department of Health issue government policy across England on DNR forms, rather than leaving it to professional guidance and policy decisions by individual NHS trusts.
That case is on behalf of the family of Janet Tracey, who died at Addenbrooke's Hospital in Cambridge. It will be heard in the High Court later this year.