The Opposition to Urban Tolling Alliance (OUTA) will on Thursday have less than 10 days to reply to government's application to the Constitutional Court.
Government has applied to the highest court in the land for the e-toll judgment to be reviewed.
It emerged on Wednesday that the South African National Roads Agency (Sanral) and the National Treasury approached the ConCourt arguing that the decision to halt the project could set a "devastating" precedent.
In his founding affidavit, Finance Minister Pravin Gordhan argued that courts should not interfere in government policies and that far-reaching and irreparable harm was being caused.
The alliance said while it was disappointed that government was going this far to defend e-tolling, it was ready to oppose the application.
Outa attorney Pieter Conradie said the court would have to decide whether it will hear the matter and whether it agrees with the urgency of it.
“If the appeal is granted then they intend to have the matter heard in the middle of July,” said Conradie.
Finance Minister Pravin Gordhan last Friday told Parliament that the Gauteng Freeway Improvement Project was not funded by government revenue.
Gordhan demanded that Sanral paid its debt through partial recovery from road users.
He also reminded members of Parliament of government’s commitment to e-tolls.
Gordhan said cabinet will be looking at all mechanisms to support Sanral which he projects will lose R200 million a month without e-toll collections.
In April, the North Gauteng High Court in Pretoria granted an urgent interdict halting the project until a full legal review was heard.
The project was due to launch on April 30, before the interdict was granted.
The African National Congress (ANC) and the Congress of South African Trade Unions (Cosatu) agreed to postpone the matter until the end of May, so that alternative funding could be investigated.
The inquiry is expected to get underway in the next few months.