Hoax phone calls are being made warning road users that their cars will be confiscated if they are not registered for the Gauteng e-tolling system, the SA National Roads Agency Limited (Sanral) said on Tuesday.

"It has been brought to Sanral's attention that road users have been contacted by people claiming to be Sanral staff members and providing users with their vehicle licence details," it said in a statement.

It urged the public to report calls to the fraud hotline on 080-020-4558, as Sanral had not instructed anyone to contact vehicle owners.

"Sanral again emphasises that nobody's vehicle can be taken away from them if they choose not to register."

Earlier, the Congress of SA Trade Unions said it would mobilise two million members to take part in national protests against the e-tolling system from April 23.

These would lead up to a large "national stay-away or socio-economic strike" on April 30, when the tolls are to be implemented, Cosatu spokesman Patrick Craven said.  -Sapa