The Constitutional Court will hand down judgment on Wednesday on a matter arising from a riot damages claim against the trade union Satawu.
The SA Transport and Allied Workers Union took the matter to court after the Western Cape High Court found the union liable for damages from a May 2006 march by striking security guards which turned violent.
Several car owners and traders who were affected brought the claim.
The Supreme Court of Appeal upheld the High Court decision.
The damages were awarded under a provision of the Regulation of Gatherings Act, which creates a statutory liability on the part of organisations under whose auspices a demonstration was held.
Satawu argued that the ruling and the wording of the act would have a chilling effect on union members' rights to organise protests and demonstrations, as it would lead to financial ruin.
The respondents, including the then minister of safety and security, contended the provisions were consistent with the Constitution.
The City of Cape Town has been joined as an intervening party and agrees with these sentiments.
The Freedom of Expression Institute sided with Satawu and was admitted as friends of the court.
The Constitutional Court will now have to decide whether the Act unjustifiably limits the right to freedom of assembly. - Sapa