There is no guarantee that members of the National Union of Mineworkers (NUM) will vote for the African National Congress (ANC) in the May 8 national general elections, the union's general secretary David Sipunzi said on Thursday.

"Remember the National Union of Mineworkers has a longstanding resolution to support the ANC -- it is a congress decision, however, it is not a blank cheque," he said at a media briefing in Johannesburg. 

"If our members down there are grumbling, we may be compelled -- having followed our Constitutional provisions -- we may be compelled to call a special national congress just to deal with that."

He said the union spends millions of rands campaigning for the ruling party. He said as the leaders of the NUM, they cannot continue with their support for the ANC when their members are grumbling and there are job loses.

"We can no longer guarantee and we are not in a position, to say without fear, that NUM members are definitely going to vote for the ANC."

Speaking on the issues at power utility Eskom, Sipunzi said the managers at the power utility should account to the board, saying the union did not want politicians "interfering" in the running of the company.

Sipunzi said there was "absolutely no consultation" with the NUM on the unbundling of Eskom ahead of President Cyril Ramaphosa's announcement in his State of the Nation Address (Sona) to Parliament on February 7. Ramaphosa had said cash-strapped Eskom would be divided into Generation, Transmission and Distribution entities as part of a new business model to help turn it around.

He acknowledged Eskom was in crisis and posed a significant risk to the South African economy, requiring bold decisions that would not affect the country's sovereign credit rating. Ramaphosa also said Eskom would need more revenue through an affordable tariff increase. 

Sipunzi said the union -- as a shareholder at Eskom -- was ignored and were shocked when Ramaphosa made his announcement. The National Office Bearers of the NUM went to the ANC headquarters and demanded answers.

"We believe that the ANC is continuing lying to us, saying that this unbundling is not going to result in job loses," he said.

He said possible investors are saying they will not invest in the power utility if the workforce is not reduced.

"The ANC knows that, and they are hiding it from us. We are [being] taken for a ride here, and we cannot tolerate that. Our members are angry out there."