The Congress of South African Trade Unions (Cosatu) says it regrets the decision of the Constitutional Court to lift the suspension of the implementation of e-tolling on Gauteng highways.

"In our view it would be a mistake on the part of government if it were to steam ahead on the basis of this Constitutional Court judgment and implement what we all now know to be an extremely unpopular policy," Zwelinzima Vavi, Cosatu secretary general, told journalists on the sidelines of federation's elective conference in Midrand.

The Constitutional Court on Thursday set aside an interim order that put on hold a plan to toll highways in Gauteng, pending the outcome of a judicial review.

"The interim order granted by the High Court on 28 April 2012, is set aside," Deputy Chief Justice Dikgang Moseneke, said, finding that the High Court had not considered the separation of powers between the court and the executive.

The North Gauteng High Court in Pretoria granted the Opposition to Urban Tolling Alliance (Outa) an interdict on April 28, ruling that a full review needed to be carried out before electronic tolling of Gauteng's highways could be put into effect.

The national roads agency, Sanral and National Treasury appealed the court order.

The national transport department welcomed the ruling.

"We want to warn government: Don't even think about it," Vavi said.

Vavi said the "legal arguments" have never been the issue and Cosatu saw the opposing of e-tolling was an attempt to "privatise" a public asset and forced motorists, including thousands of workers, to pay double to get to and from work.

Cosatu has engaged both the government, in the person of Deputy President Kgalema Motlanthe, and the ANC, in a joint task team to investigate alternative and better ways to fund road construction and improvements.

"We warn the government not to even think about implementing e-tolls until these consultations have been completed. Should they do so Cosatu will oppose them with every power we have," he said, warning that the federation could resort to mass demonstrations.