The SA National Roads Agency Limited (Sanral) must disclose the names of all 33 sub-contractors involved in the collection of e-tolls on Gauteng highways, the DA said on Sunday.
"This is after disturbing reports [on Sunday] about African National Congress links to companies that will benefit from the e-tolling," Democratic Alliance spokesman Jack Bloom said in a statement.
The DA has asked Public Protector Thuli Madonsela to investigate the controversial Gauteng e-toll collection contracts.
On Sunday, Bloom said he had received acknowledgement of his request.
"It is vital that this investigation goes ahead so that we know the truth about who benefits from these controversial contracts, and whether there was any corruption," he said.
The Sunday Times has reported that politically-connected companies stand to benefit from e-tolling contracts.
According to the newspaper, these included Tsebo Holdings, South Africa's largest catering company, which was 15 percent owned by Nozala Investments and 15 percent by Lereko.
The Sunday Times reported that Nozala was headed by Salukazi Dakile-Hlongwane, a trustee of the ANC front company Chancellor House, and that Lereko was owned by former environment minister Valli Moosa and Chancellor House trustee Popo Molefe.
Other companies which stood to benefit were Vodacom and GijimaAST, which was 35 percent owned by billionaire businessman Robert Gumede, which won the two largest sub-contracts.
JSE-listed Gijima was awarded the contract to design and run the project's IT system, the Sunday Times reported.
Molefe was reportedly not aware that Tsebo had any e-tolling contract until told of this by the Sunday Times.
"We as Lereko has not been involved in any discussions about e-tolling. We're not even on Tsebo's board, so we have no influence," he told the newspaper.
The 33 sub-contractors were signed up by the electronic toll consortium (ETC), after it was awarded the main R6.6 billion contract by Sanral in 2009. The ETC is responsible for collecting e-tolls.
The Sunday Times reported that the ETC had provided it with the names of only nine of the sub-contractors this week.
In an interview with the Sunday Times, ETC chief executive Salahdin Yacoubi said he would not release the full list of sub-contractors until he had "obtained permission" from them.
He said he had "nothing to hide" and would "collaborate with any investigation" into the beneficiaries of the e-toll contracts.
The Sunday Times also reported that a major beneficiary was the Swedish company Kapsch TrafficCom, which owned 40 percent of the main contractor.
The company confirmed to the newspaper that, until 2000, it was owned by arms company SAAB, which admitted in June to paying bribes of more than R24-million to ensure it was picked to supply Gripen jets to South Africa in the arms deal.
The e-tolling system was halted last Saturday until a full court review could be carried out to determine whether it should be scrapped.