Cosatu promised on Wednesday it will "take to the streets" if Eskom is allowed to increase its electricity tariff by 35% a year for the next three years.

The federation's provincial secretary in the Western Cape, Tony Ehrenreich, said at a hearing by the National Energy Regulator of South Africa in Cape Town, that the proposed tariff increase would close down half of the manufacturing sector.

"No increase that exceeds inflation should even be contemplated," Ehrenreich said.

"If need be we will take to the streets with the affected communities to protest against it."

Ehrenreich proposed a "solidarity pact" on the wealthy to help Eskom fund its infrastructure expansion program.

Ehrenreich said the increase would plunge poor people into enormous difficulty.

He said there was "obvious extravagance" in wealthy communities.

"We should tax the wealthy so Eskom can fund its programme."

Eskom acting chairman Mpho Makwana told the hearing that a 35% increase every year for the next three years was vital for Eskom's infrastructure programme.

"Eskom can only do what it can with the means that are available to it financially," he said.

"We have to ensure that we don't over stretch ourselves and compromise the country's continuity of supply."

He said Eskom had not been building its financial reserves. Some equity had come in from the government, but it was not enough.

"An appropriate tariff for South Africa to continue to function optimally is 35% a year for three years," he said.