The UK's Equality and Human Rights Commission (EHRC) confirmed that it had applied for an injunction against Wilson at the Central London County Court.
"We have asked the court if it agrees with us that Mr Wilson's lettings policy contains unlawful criteria and, if so, to issue an injunction," said EHRC chief executive Rebecca Hilsenrath.
"As this is now formal legal action we will release further information at a later date," she said.
However, Wilson remained defiant over his policy, which he justifies on economic grounds to save costs on re-carpeting homes that smell of Indian cooking, once tenants have left.
"Given that I have not had any Indian or Pakistani person apply for a house during the past five years, I am not sure what the EHRC seeks to achieve," he said.
"It is not the colour of their skin, but the smell of the curry. A person is quite entitled not to purchase a house that smells of curry but to purchase the house next door which does not smell of curry. The EHRC appears to be saying that the purchaser then must let the house to someone who does cook curry," he added.
The former boxer, whose property empire in Kent includes around 1,000 homes in the Ashford and Maidstone areas of south-east England, denied he was being racist.
"There has been much support for the stance I have taken. I do not apologise for it. Faced with the same circumstances, I would do it again," he said.
The EHRC had demanded a written assurance from Wilson that he would not refuse to let a property based on race, colour, nationality or national origins.
It said it would now begin an investigation into his policy on women as it emerged his lettings criteria also covers a ban on single parents, "battered wives", parents with children under 18.
His stand had emerged as an email to his agents was leaked to the media earlier this year.
"No coloured people because of the curry smell at the end of the tenancy," it read.
According to the UK's Citizens Advice Bureau, refusing to rent or let a property based on race is unlawful.