The DA has asked Public Protector Thuli Madonsela to investigate the controversial Gauteng e-toll collection contracts.
"Suspicion is high that politically-connected people may have benefited from the toll companies contracted to SA National Roads Agency Limited (Sanral)," Democratic Alliance MPL Jack Bloom said in a statement on Thursday.
"Widespread public concern needs to be allayed by a full investigation by the Public Protector."
The Electronic Tolling Collection (ETC) consortium is the company responsible for collecting toll fees.
Bloom said there were reportedly allegations of links between Swedish companies involved in an arms deal, and Vienna-based Austrian company Kapsch TrafficCom, which was the largest shareholder in ETC.
"In giving the background to his interdict against the e-tolls, Judge Bill Prinsloo criticised Sanral for its secrecy on the contract with the ETC consortium," said Bloom.
"There are also 35 sub contracts with ETC, all with confidentiality clauses."
On Saturday, Prinsloo granted an urgent interdict, brought by the Opposition to Urban Tolling Alliance, to stop the e-tolling system so that a full court review could be carried out to determine whether it should be scrapped.
Prinsloo said that while he realised Sanral would suffer huge financial losses, the public would also suffer hardship if the controversial project went ahead.