Plans to ban white people from becoming Labour candidates in winnable seats will be divisive, MPs have warned.
Labour MPs in Birmingham said proposals to introduce ethnic minority-only shortlists could damage race relations in the city.
The scale of the opposition suggests Labour's Deputy leader, Harriet Harman, faces a battle with her own backbenchers if she presses ahead with the plans.
She is currently examining a report produced by Simon Woolley of Operation Black Vote, which warned positive discrimination was needed to make Parliament more representative of the country as a whole.
The report follows an inquiry launched by Ms Harman last year, when she told the Labour Conference that she wanted to allow all-black shortlists in constituencies with high ethnic minority populations.
The next stage is likely to involve the introduction of legislation in the House of Commons, because ethnic minority-only shortlists are illegal.
Ms Harman wants the short-lists to be used in regions with a high level of ethnic diversity, such as the West Midlands.
One in five people in the West Midlands county are members of a visible ethnic minority, according to the 2001 census. But the county, which includes Birmingham, Coventry, Wolverhampton and the rest of the Black Country, only has one black or Asian MP out of 29.
However, Labour's existing MPs warned there would be hostility to the plan. Siôn Simon (Lab Erdington) said: "We do need more ethnic minority representation in Parliament.
"But at the council level, we are not doing too badly. And we have got there while preserving a relatively harmonious atmosphere on these kinds of issues. All-ethnic minority shortlists risk upsetting that balance."
Roger Godsiff (Lab Sparkbrook & Small Heath) said: "I have always believed that members of the Labour Party, when choosing candidates at a local or national level, should choose the candidates they believe are best able to represent them and best able to carry out their responsibilities, irrespective of race, religion, colour or gender."
And Khalid Mahmood (Lab Perry Barr) said ethnic minority-only shortlists would be seen as "segregation". He said: "This would be divisive. A candidate has to represent the whole community and not be seen as the candidate for one part of it."
Even MPs who backed the proposal had concerns.
Richard Burden (Lab Northfield) said: "While this raises difficult issues, we do need to make Parliament more representative of the country and I would not rule out the idea. However there are questions which need to be answered, such as how exactly we define who is part of an ethnic minority. I am not sure it could be done, in practice."
Mr Woolley's report calls for ethnic minority-only shortlists to be used for the next 20 years in some constituencies.
There are only 15 MPs from ethnic minority backgrounds in the House of Commons, 13 on the Labour benches and two in the Conservative Party.
If the number reflected the proportion of people from ethnic minority backgrounds in the UK as a whole, it would increase to 58.
Midland peer Lord Taylor of Warwick (Con), one of the few black members of the House of Lords, recently warned that Britain was failing to develop a home-grown equivalent of Barack Obama, the black presidential hopeful.
He said: "A black American president was more likely to happen before a black Prime Minister."
Liberal democrat leader Nick Clegg last night backed proposals for all-ethnic minority shortlists.