The Commission for Racial Equality has been asked to intervene to ensure black and Asian teachers get a fair deal on pay, The TES can reveal.
Official figures released to the National Union of Teachers show that white British teachers are far more likely than other ethnic groups to pass the threshold and add thousands of pounds to their salary.
Fewer than one in 20 white British teachers who applied to cross the threshold failed to do so during round four in 2004, the latest for which figures are available.
This compared to one in five teachers of Bangladeshi and black African origin and one in 10 teachers of Pakistani, Indian and Black Caribbean origin.
The NUT obtained the figures using the Freedom of Information Act. Steve Sinnott, the union's general secretary, said schools have "a case to answer in relation to unlawful discrimination on the grounds of ethnicity".
There are no comparable statistics for round five of threshold applications, held last year, because of the decision by ministers to stop double checking schools' decisions.
Mr Sinnott said that the Government is now failing to fulfil its legal duty to monitor whether teachers from different racial groups are being treated equally by schools.
Discrimination may also have occurred when schools carried out staffing reviews ahead of the introduction of teaching and learning responsibility payments, he said.
The Government turned down a request from the NUT for schools to assess the impact of the changes on racial and gender equality as part of the review.
The replacement of management allowances with TLRs will cost some teachers up to pound;10,500-a-year though others will gain thousands. Teachers at the top of the upper pay spine earn pound;4,600-a-year more than their colleagues who have yet to pass the threshold.
During an exchange of letters, Ms Kelly admitted the end of external assessment of threshold applications last year made it impossible to check how different ethnic groups were faring.
But she said the available data did not prove there was a problem: "Success rates do vary from year to year and between different minority ethnic groups but it is difficult to draw any firm conclusions. The success of white British applicants is not necessarily the highest."
Ms Kelly said a new school workforce database would help monitor the situation and said she was "open to constructive representations on the matter".
The NUT wants the General Teaching Councils in England and Wales to be asked to monitor whether schools are guilty of racial discrimination. It also wants teachers who fail to gain promotion to be given the right of external appeal against the decision.
Mr Sinnott said that without action, ethnic-minority teachers might be discouraged from applying for promotion.
"That would be a classic sign of institutional racism. The Government appears complacent about the situation."
Steve Sinnott: the Government is now failing to fulfil its legal duty to monitor equality between racial groups