Her remarks undermined international investor confidence Leon said in an internet letter.
Leon stated: "Yesterday, she threw another racist tantrum, accusing South Africa's largest companies of retaining too many white management staff," noted Leon.
Xingwana said about De Beers: "Today we again express our exasperation and disappointment by De Beers's announcement that it will replace one white male managing director with another white male managing director.
"This is the same company whose board of directors is lily-white and male-dominated. No single black South African is in the board.
She was referring to the retirement of Gary Ralfe as managing director next year and his replacement by Gareth Penny.
Xingwana also criticised Anglo American for appointing Lazarus Zim - a black man - as the company's South African CEO while Tony Trahar remained CEO of Anglo plc.
Previously Trahar held both jobs.
She also criticised Sasol for being slow to transfer 18% of equity into black hands in compliance with the requirement with the liquid fuels black economic empowerment charter.
Leon said in response that "while the (ruling) African National Congress's recent discussion documents talk of economic reforms - including deregulation of the labour market - the deputy minister's outburst revealed the true priorities at the core of the ruling party's economic policy: Race and power.
"This government apparently believes that it has the right to have a say in the affairs of private companies, forgetting that the business of government is not the government of business.
"And it also apparently believes that race is the only qualification that is important for senior management posts.
Certainly that would seem to apply in the case of deputy minister Xingwana herself.
"In South Africa, when deputy minister Xingwana uses language worthy of the worst excesses of the apartheid regime to attack major companies, the business community is silent and local newspapers hesitate to offer criticism."
The deputy minister did not know or care "that her racist statements actually hurt black South Africans as much as white South Africans, by discouraging investor confidence in our country."
Last September, Xingwana conducted a stinging attack in Parliament on "white capitalists" whom she accused of having in the past stolen South Africa's mineral wealth.
She accused "white capitalists" - and companies - of "getting rich" out of illicit gains from the country's mineral wealth.
Referring to the black economic empowerment charter, she said last year that it aimed to ensure "a meaningful share" in mineral wealth.