GP exam pass rates are being investigated by the General Medical Council after claims of discrimination from foreign-trained doctors.
They claim they are facing institutional bias and are unfairly failing GP exams despite extensive training and knowledge.
The GMC said it was "determined to understand the issue".
The Department for Health said it could not comment while the investigation was taking place.
The doctor's watchdog has begun an independent review into the "disproportionate" failure rates for internationally-trained and British-trained ethnic minority medical graduates taking Royal College of General Practitioners (RCGP) examinations.
Chief executive of the GMC, Niall Dickson said: "Where serious questions have been raised, as they have in this case, it is right that we should look at them.
"The underlying causes for different pass rates among different groups of doctors are likely to be complex, but we are determined to understand the issue."
The review will also look at the Clinical Skills Assessment, a practical and knowledge-based test introduced in 2010 in which candidates treat people posing as patients.
It takes several years to train to become a GP after gaining a degree, and in their final year students must pass the CSA before they can qualify.
Figures published by the RCGP show that 65.3% of foreign-trained GPs failed their first attempt at the CSA in 2011-12, compared with 9.9% of medical graduates who studied in the UK.
Concerns have also been raised about different pass rates for black and minority ethnic UK-qualified doctors.
The failure rate for British medical graduates of South Asian origin is 17.5% and for a black candidate 24.4%, compared with 5.8% for a white candidate.
The RCGP said: "We take equality and diversity issues very seriously and strongly refute any allegations that the MRCGP exam is discriminatory.
"Our assessment procedures, which are designed to ensure safe patient practice, have been approved by the General Medical Council, as the regulator - and we welcome their current review into the matter and are working together with them on it."
Kailash Chand, deputy head of the British Medical Association, said: "We cannot ignore the disproportionately high failure rates for international and ethnic minority doctors.
"This is not just an issue for GP exams but across medical exams in the NHS and we need to get to the bottom of it."
Dr Akmal Makhdum, chair of the British Pakistani Doctors Forum said the "stark statistics" made the exam stand out.
"The significantly different pass rates cannot be explained by a lack of knowledge, skills or competency.
"There is no doubt that there is indirect race bias and discrimination at play which would explain why highly-qualified doctors, who have been working in the NHS for a number of years, are failing.
"Many foreign doctors have ended up losing their jobs and lost thousands of pounds attempting to qualify as GPs."
The highest failure rates taking the GP exams are for candidates trained in South Asia, with 69.4% of candidates failing their first attempt at the CSA.
Raj Singh, a medical graduate from India, who has been working in the NHS for several years, took the exam four times and failed at each attempt.
"I do not understand how I was unable to improve my marks in four attempts," he said.
"I have no more attempts at the exam and my three years of training as a GP have been a complete waste of time and money.
"It has taken a serious strain on my physical and mental health; at one point I was extremely depressed."
He added: "It is very hard for people who have not gone through it but I strongly believe there is a strong element of discrimination."
However, some GP trainers claim the failure rates can be explained by language and cultural difference for overseas candidates.
Dr Jagroop Sihota, a British Asian GP from Coventry who helps train medical graduates taking GP exams said he did not think doctors trained overseas were being discriminated against.
"It is acknowledged that there is a high failure rate for overseas doctors, but in some ways that is to be expected because they are from a different cultural background.
"They do find it difficult to relate to British patients."
He added: "You have to look at the people who fail exams; they always look to blame other people."
The GMC's review is expected to be completed and published later this summer.
A spokeswoman for the Department for Health said: "While the investigation by the GMC is taking place and the findings have not been published we are not able to comment on the concerns raised by foreign doctors working within the NHS."
Listen to more on this story on BBC Asian Network on 10 July.