Cosatu has long protested the implementation of e-tags on South African roads.
"Don't register! Don't buy e-tags!" the Congress of South African Trade Unions said on Thursday.
Spokesperson Patrick Craven expressed disappointment at the judgment and said Cosatu would approach Parliament and continue its mass action.
He said tolls would add to the burden on the poor and affect motorists in other provinces once the transport department rolled tolling out across the country.
"Tolls will also put an indirect burden on the poor of the whole of South Africa, by adding to the cost of transporting goods, and will have an immediate effect on food inflation."
Craven said the system would see a large portion of the revenue going into the pockets of toll operators.
On Thursday, Judge Louis Vorster found the Gauteng Freeway Improvement Project (GFIP) was lawful and dismissed an application by the Opposition to Urban Tolling Alliance (Outa) to have e-tolls on Gauteng's highways set aside.
He said the application could not succeed and ordered Outa to pay costs.
'Do not take the government to court'
Anti-toll activist Rob Handfield-Jones said the consultation done in 2012 proved the public had very little understanding of the implication of e-tolls in 2007.
"South African National Roads Agency Limited's [Sanral] version of 'consultation' was akin to getting someone to agree to a dam being built nearby without telling them their house would be flooded when the dam was filled," he said.
"Using Sanral's figures, GFIP has cost R113-million per kilometre to build. How is this possible for what amounted mostly to large-scale re-surfacing?" Handfield-Jones called on road users to reject the "unjust and uneconomical system" and to not buy e-tags.
"Do not pay toll fees. The system relies on voluntary compliance … It will be impossible to prosecute tens of millions of offences per month."
The Justice Project South Africa expressed concern at the decision to order Outa to pay the legal costs for Sanral, the transport department, treasury, the Gauteng roads and transport provinical minister, minister of water and environmental affairs and the department's director general.
"Given the fact that government has spent [an] estimated … R30-million of taxpayers' money on defending this matter, should Outa have to pay government's legal expenses, there is no doubt that Outa will not be able to do so," chairperson Howard Dembovsky said in a statement.
"This will expose the directors of Outa to be held responsible in their personal capacities."
"This will send a very clear message to non-governmental organisations not to take government on in court, regardless of how good their case may be, just in case they lose. The judgment sent the message "don't screw with government or you will be bankrupted".
Anti-e-toll campaign continues
Freedom Front Plus spokesperson Anton Alberts said the campaign against e-tolling would continue.
Outa's chairperson Wayne Duvenhage said they were still not sure whether to appeal or take the matter to a higher court.
Transport director general George Mahlalela said it was unclear when the minister would make the implementation announcement, but that it would not happen in 2012.
"There will still be people who are unhappy with the outcome and there is nothing we can say. If people opt for civil disobedience we hope they will not do illegal things."
Earlier, the government and Sanral welcomed the decision and urged motorists to buy e-tags.
Earlier legal battles
The contentious 185km stretch of Gauteng roads planned for e-tolling has been subject to a number of legal battles and Outa in fact appeared to be gaining ground earlier this year when an urgent interdict against the implementation of the project was granted.
Vorster, in handing down the judgment ruled that the necessary public consultation had in fact taken place, said the matter of financing of the project did not require the consent of the public.
Nazir Alli, chief executive of the defendant, Sanral, said he hoped the public would now respect the court's decision.
The tolling system requires commuters to fit an e-tag that will monitor each time they pass a gantry on the highway and be charged electronically.
Vehicles without an e-tag will have their licence plates monitored and billed for their journeys.
If people refuse to pay their bill, they will be barred from renewing their vehicle licenses until all outstanding fees have been paid. – Additional reporting by M&G Reporter