A surgeon at a London NHS hospital wore a Palestine badge while operating on a Jewish patient.
The patient, who had an operation at the Royal Free Hospital in Belsize Park, north London, last month, was left "extremely distressed" after spotting the badge on the staff's lanyard.
She said she "found it extremely stressful to be treated by this doctor, given her blatant political views" and that "she felt that the doctor could do her some harm".
It comes just weeks after Wes Streeting, the Health Secretary, said he would ban NHS staff from displaying pro-Palestinian badges as part of a crackdown on anti-Semitism in the health service.
In a letter to the Board of Deputies of British Jews in May, Mr Streeting vowed to snuff out "the appalling experiences of anti-Semitism affecting Jewish staff and patients" in the NHS.
UK Lawyers for Israel (UKLFI), which the patient contacted after the operation, accused the Royal Free London NHS Trust of breaching equality legislation.
In a letter to trust bosses, the group said staff wearing the Palestine flag badge could constitute harassment by the hospital, breaching Section 29 (3) of the Equality Act 2010, since it may create "an intimidating, hostile, degrading, humiliating or offensive environment" for Jewish patients.
UKLFI said the incident and the display of a Palestine badge "indicates support for the Palestinian cause, and conversely, opposition to the State of Israel".
The lawyers' group said the surgeon, who has not been named, was "prioritising her own political opinions over care and empathy for her patients", which breached General Medical Council (GMC) regulations.
A spokesman for UKLFI added: "It is important that the hospital staff abide by the principles of political neutrality, as not doing so can harm vulnerable patients.
"We hope that the hospital staff who break these rules and blatantly display their political affiliations will be appropriately disciplined."
In a letter, David Crampsey, chief executive of the Royal Free London Foundation Trust, said the concerns "were being looked into and that the trust will consider any appropriate action having done so".
Mr Crampsey said the trust was "committed to creating a positive culture of respect for all individuals, including job applicants, employees, patients, and their families".
Staff, he said, were reminded of "the principles of political neutrality in relation to their work", adding he was "deeply saddened" to hear that the patient felt that the doctor could do her some harm.
The trust operates the Royal Free Hospital, Barnet Hospital, Chase Farm Hospital, and North Middlesex University Hospital.
Staff at some of London's biggest NHS hospitals have already been banned from wearing pro-Palestine symbols after complaints that they were "upsetting and intimidating" vulnerable patients.
Barts Health NHS Trust confirmed the decision earlier this year after UKLFI said growing numbers of Jewish patients were reporting their distress at seeing clinical and medical staff wearing provocative slogans and badges in Palestinian colours.
The trust's ban applies to its five hospitals: St Bart's, Mile End, Newham, Royal London, and Whipps Cross.
UKLFI raised the case of a young Jewish woman who attended Whipps Cross for a caesarean and encountered three members of staff wearing pro-Palestine badges in a 24-hour period.
In January, an outpatient receptionist at Royal London Hospital was seen wearing a black T-shirt showing a Palestinian keffiyeh scarf covering the map of Israel.
The Telegraph has approached the GMC and the Royal Free London NHS Trust for further comment.