The British Medical Association (BMA) said it had serious concerns that patients could be put at risk by new proposals from the European Union (EU).
At present, each member state regulates their own health care system, setting standards, clinical guidelines and rules on qualifications for doctors.
The BMA said that whereas at present, doctors working in the UK are regulated by the General Medical Council, under the EU proposals a doctor working in the UK who had qualified in another EU country would effectively be regulated by their home country.
Dr Edwin Borman, head of the BMA's international committee, said: "These new proposals undermine each member state's ability to decide what is in the best interests of its patients and its healthcare systems”.
