Opposition parties are calling for the ANC to disinvest its stake in a company contracted to help build two new Eskom power stations.

A statement from the Democratic Alliance on Wednesday said the ANC, which has admitted to owning a 25% share in Hitachi South Africa, would benefit from a deal worth nearly R6-billion.

"With the ANC's stake in Hitachi it is only reasonable to believe that steep electricity price increases by Eskom will benefit the ANC's party coffers," party MP Sej Motau said.

"If the ANC can own shares in companies that provide services to parastatals, then the ANC government's so-called developmental state model boils down to naked cronyism and a systematic exploitation of South Africans."

ANC secretary general Gwede Mantashe is reported to have said this week that the party still owns a 25% share in Hitachi South Africa.

The party's treasurer, Mathews Phosa, promised to take steps to disinvest the party's interest last year.

"Mr Mantashe's claim that there is nothing wrong with the ANC's interest in the company shows his disregard for the interests of a democratic society and the constitutional principles of accountability and transparency," Motau said.

Independent Democrats spokesman for energy, Lance Greyling, said this week that much of Eskom's proposed 35% electricity tariff increase per year for three years would be used to fund the construction of the coal-fired Medupi and Kusile power stations, in Limpopo and Mpumalanga.

"The biggest component of this expenditure is for boilers for the two power stations, a contract worth R38-billion (in 2008) that was awarded to Hitachi Africa which the ANC's front company, Chancellor House, had a 25% stake in at the time," Greyling said.

"This means that through Chancellor House the ANC's share of the deal was worth R5,7-billion, notwithstanding the fact that since then cost estimates have almost doubled.

Greyling said current estimates were that costs had risen from R78-billion to R120-billion and R85-billion to R142-billion for Medupi and Kusile respectively.

"The ID calls on the ANC to provide proof that it has lived up to its promise and that consumers will not be indirectly funding the ANC through the proposed electricity price increases."

Comment from the ANC was not immediately available.