Cabinet's decision to appeal against the High Court in Pretoria's interim order against e-tolling was condemned by opposition parties on Thursday.
The African Christian Democratic Party (ACDP) described the decision as "regrettable".
This would further delay the finalisation of litigation around the project.
"We believe the review application would shed important light on various issues, including the contacts relating to the cost of collection," said ACDP spokesman Steve Swart in a statement.
"It is significant that the minister of transport has requested copies of various contracts, indicating that he too was unaware of the exact costs of collection."
Swart said the ACDP would inquire whether the National Treasury would bail out the SA National Roads Agency Limited (Sanral), and if so, to what extent this would be.
"It seems at the end of the day the taxpayer will have to pay for this debacle, either in the form of user charges, should the court challenge be unsuccessful, or in the form of a bail-out from National Treasury," he said.
The Freedom Front Plus said the government was showing its contempt for taxpayers with its decision to appeal.
"Government is trying to prove a point with taxpayer's money," said FFPlus spokesman Anton Alberts in a statement.
"Government did not consider road users before the Gauteng e-toll system was constructed and is now ignoring the overwhelming opposition by taxpayers and road users to the toll roads."
His party was of the opinion that there were not sufficient legal grounds for the government to succeed in its appeal.
The Justice Project of SA (JPSA) expressed disappointment at Cabinet's decision.
It was sad to see the government persist with its stance in the face of such overwhelmingly public opposition, it said.
"We also need to ask whether the intention to appeal the interdict has anything to do with an attempt to halt a full inquiry into the project in order to cover up possible corruption or not," it said in a statement.
It called for the issue to be put up for referendum.
"A ring-fenced fuel levy will achieve the objectives of paying for these roads and others still to come in a far more efficient and less costly manner," it said.
The Democratic Alliance said Cabinet's decision to appeal was "foolish and doomed to fail".
The interim order issued by Judge Bill Prinsloo was unlikely to be overturned, as sound reasons had been given for it, DA spokesman Jack Bloom said.
"Government's appeal will just drag out the court proceedings, creating further uncertainty in the credit markets."
He was puzzled by the government's hard line, as Sanral had itself indicated it would not appeal the case.
"It would be far better if government cancelled the e-toll collection contract, rather than continue with a long, drawn-out court battle," he said.
Cabinet spokesman Jimmy Manyi said earlier the government would appeal against the interim order. He said the government only received a written copy of the April 28 judgment late on Wednesday.
"As we are sitting here, our lawyers are studying the judgment and will advise the executive in due course," he told a fortnightly post-Cabinet briefing.