The South African government intends to cancel the registration of the Association of Mineworkers and Construction Union (AMCU) for not operating according to the Labour Relations Act, a notice in the government gazette said on Wednesday.

AMCU, one of the largest trade unions in South Africa's mining sector, has thousands of members at gold and platinum mines operated by companies including Sibanye-Stillwater and Lonmin.

It is known for its uncompromising stance after leading a bruising strike in the platinum sector. Last week it ended a five-month walkout that cost Sibanye-Stillwater more than $100-million in lost revenue.

The notice in the government gazette said: "I, Lehlohonolo Daniel Molefe, Registrar of Labour Relations, ... give notice of my intention to cancel the registration of Association of Mineworkers and Construction Union."

Giving reasons, Molefe said: "The trade union has ceased to function in terms of its constitution and the trade union is not a genuine trade union as envisaged in the Act."

Attempts to reach a spokesperson for South Africa's labour ministry by phone to get a further explanation of Molefe's position were unsuccessful.

An AMCU representative said the union's leader, Joseph Mathunjwa, was not available for comment.