A court application was filed on Friday to stop tolling in Gauteng, the Opposition to Urban Tolling Alliance (Outa) said.

"It is a sad day when a nation's government develops a tense and threatening relationship with its people, when trying to force an unjust and unpopular decision into being," group spokesman Wayne Duvenage said.

The fuel levy could be used to pay for the Gauteng Freeway Improvement Project at an additional cost of between eight and ten cents per litre of fuel, he argued.

If tolling of major roads in Gauteng went ahead, other provinces could expect the SA National Roads Agency Limited (Sanral) to finance their roads in the same way.

Duvenage said between 25% and 30% of Gauteng's four-million vehicles used the proposed toll routes daily.

Sanral itself estimated there would be 2.5-million transactions every day. Around 10% of number plates were incorrect, which would result in some vehicle owners being liable for charges they did not incur, said Duvenage.

Pieter Conradie of law firm Cliffe Dekker Hofmeyr said Outa wanted an urgent interim interdict from the High Court in Pretoria preventing Sanral from levying tolls on Gauteng highways.

Tolling is scheduled to start on April 30, according to the court papers. Outa's application is scheduled to be heard on April 24, Conradie said.

The alliance also wants the court to set aside the decision to toll.

Court papers were being served on Sanral, as well as Transport Minister Sbu Ndebele, Water and Environment Affairs Minister Edna Molewa and her director general, Gauteng transport MEC Ismail Vadi, and the National Consumer Commission, Conradie said.

The Democratic Alliance welcomed the move.

"This is a very exciting development that we believe will force the government to reconsider the tolls," DA Gauteng spokesman Jack Bloom said.

Outa is composed largely of motoring industry associations, including the Retail Motor Industry and the SA Vehicle Rental and Leasing Association. The SA National Consumers' Union (Sancu) and the Quadpara Association of SA are also supporting the application, their representatives said.

Sancu spokesman Cliff Johnson said the union believed the public participation process that led to the decision to toll Gauteng's roads had been inadequate. It objected to the "agreement" between consumers and Sanral, which placed the onus on consumers to prove they were not liable for fees Sanral charged.