The Advertising Standards Authority of South Africa is investigating the TV Omo Challenge in which mothers are invited to wash dirty shirts for the chance to win bursaries for their children.
A row blew up after two white women each won 50,000 rand (£4,000) while another contestant, a black woman at a Johannesburg children's home, won 10,000 rand.
"What they show is that it's a privilege for blacks to win, while it's a right for whites," a letter to the City Press newspaper complained.