Arguing an application by the South African Transport and Allied Workers' Union for leave to appeal an earlier judgment on damages, Advocate Wim Trengove said the law set out that liability was premised on reasonable steps being taken to avoid unforeseeable harm.

He told the court that "reasonable", by its nature, could never be inclusive of all the risk attached to a protest. The nature of a protest was to air grievances, and it was a confrontational and often explosive act.

The union went to the Constitutional Court to challenge a recent High Court ruling that held it responsible for damages caused during a march in Cape Town. The ruling was upheld by the Supreme Court of Appeal.

It contends that parts of the legislation on the wording regarding freedom of assembly are unconstitutional.

Trengove questioned whether a protest against racism through the North West town of Ventersdorp should be cancelled - a violation of the right to protest - if there was a direct physical threat from members of right-wing organisations.

He said a union could bring in more people to maintain calm, but it could not absolutely promise that the march would remain peaceful.

He conceded that the union was liable in some instances where it acted unlawfully. However, this could not be the case where it did not "knowingly cause" harm.

"The union is not at fault, the perpetrators are. The legislation is sloppily drafted," he said.

The union, supported by Cosatu, feels the legislation imposes undue responsibility on organisers of a gathering. It holds that this is undemocratic in that it limits protest, which is often the only way people can make their voices heard.

The City of Cape Town joined the matter as an intervening party. It supports the eight respondents.

The Freedom of Expression Institute was admitted as a friend of the court.