Cosatu general secretary Zwelinzima Vavi told a workers' march on Wednesday that should government go ahead with e-tolling, workers would block freeways.
The e-toll freeway billing system is set to be introduced on April 30.
Johannesburg Metro Police Department's spokeswoman, Edna Mamonyane warned yesterday that police would deal harshly with people who broke the law.
"The law says no pedestrians are allowed on the freeway. Blocking the freeway will be an unlawful act and they will be arrested because they will be breaking the law," she said.
Cosatu spokesman Patrick Craven was adamant that workers would defy the law and block the freeway unless government scrapped them before April 30.
"Judging by the numbers from Wednesday's march, it will be impossible for police to arrest us. We will go ahead with the march if government does not change its mind," said Craven.
Meanwhile, Cosatu yesterday warned labour brokers not to victimise workers who joined the protest march saying the work stoppage was legal.
"We have been inundated with reports of threats to workers who participated in the strike. Cosatu calls on workers who have been threatened by labour brokers to report such unfair labour practices to the federation," said Tony Ehrenreich, Cosatu Western Cape provincial secretary.
The South African National Roads Agency Limited (Sanral), accused unnamed political and civic leaders of misleading the public about the payment of toll fees.
"Sanral has noted with concern untruths being propagated by some political and civil organisation leaders trying to gain support for their grievances around e-tolling," it said in a statement.
Sanral also denied that it would have access to the private bank accounts of registered e-toll users. It said the automated credit card payment system did not give it access to account holders' bank accounts. Rather those who registered for this type of payment could regulate their accounts by setting pre-determined top-up threshold levels.
"If motorists were unsure about giving their credit card details for payment of toll fees, they could use a pre-paid e-toll account," the statement said.
"This meant they could top up their e-toll account at a customer service outlet or via electronic funds transfer. This is already widely used by other organisations."
The roads agency also warned that 1200 people stood to lose their jobs if the e-tolling system was scrapped.
Finance Minister Pravin Gordhan announced recently that tariffs for Gauteng's toll gates had been reduced to 30c per kilometre for light motor vehicles with an e-tag. - additional reporting by Sapa