Not paying toll fees is against the law, regardless of whether an invoice is issued, Sanral said on Sunday.
"Not paying your toll fees is not just a traffic offence, but a criminal one," SA National Roads Agency Limited (Sanral) spokesperson Vusi Mona said in a statement.
"The legal obligation to pay [the] toll arises from using the toll road and passing underneath a gantry, not from an invoice that is forwarded to the road user."
"Sanral is using legally available resources at its disposal to contact vehicle owners. We are issuing notices, with invoices to follow, in order to alert road users that they have outstanding debt."
Anyone who said otherwise was "misleading" the public, he said.
He said the courts had already ruled on matters relating to e-tolls.
"It is regrettable that there are some organisations which are still contesting the legality of e-tolling outside court processes."
Earlier this week, the Justice Project SA (JPSA) urged Sanral and the transport department to go to court to seek legal clarification as to the validity of conflicting tolls tariffs published in the Government Gazette.
The English and Afrikaans versions of e-toll tariff notices published in the gazette differed in the amounts stipulated.
"It is not for anyone to prove the lawfulness of acting under invalid legislation, but for the department to obtain confirmation of the high court as to clarity thereof and enforceability of the administrative action based on conflicting legislation." said JPSA chairperson Howard Dembovsky.
However, transport department spokesperson Tiyani Rikhotso said at the time that the "noted mistake in question won't affect the validity of the legislation".
Dembovsky then suggested the department was trying to "wish away their 'mistakes'".
The Star newspaper reported that, according to Dembovsky, users of the paymyfines website were receiving e-toll bills by email even though they were not registered e-tag users, or had not given their email address to Sanral.
The newspaper reported that its own investigation had found that the company running the paymyfines website and the website etcrecovery.co.za, which was sending the emails demanding etolls, were part of the same company — TMT Services.
A South African company, TMT, was part of the Austrian company Kapsch TrafficCom, which runs the e-toll project.
At the time, Mona said that Sanral was obtaining information for invoices from eNatis, the national administration traffic information system, and from a "database legally obtained from third parties".