South Africa's Deputy Education Minister Mduduzi Manana has been accused of hitting a woman during a row at a nightclub.
Mr Manana has apologised for the "shameful incident" saying that even though he was provoked, he "should have exercised restraint".
Women's minister Susan Shabangu said she heard the news of the alleged assault "with great shock".
There are concerns about the level of violence against women in the country.
A police spokesman confirmed to Agence France-Presse that they were investigating the alleged incident, which took place in the early hours of Sunday morning.
'Accused of being gay'
In a tape recording leaked to the press, purportedly of a conversation between the victim's brother and the minister, the person alleged to be the minister admits to slapping the victim when she called him gay.
But he implies that other people who were with him were responsible for the worst of the violence.
Lumko Jimlongo, a journalist from the national broadcaster SABC, witnessed the alleged assault at the Cubana nightclub near Johannesburg.
He told SABC news that the victim was trying to walk towards the exit when she was struck, "she fell on the floor... then he proceeded to trample [her]... and his foot was on her head".
Mr Manana made his apology "to the victim, her family... and all South Africans" and said that he hoped to speak to her personally to "address the harm that has occurred".
Local media report that the row started over who should succeed President Jacob Zuma when he steps down as leader of the governing ANC in December.