The Labour Court is due to rule on Friday morning whether 42000 Satawu members at two Transnet divisions may legally go on strike next week.
The decision could either open or close the door on wide-ranging strikes in sympathy with road transport workers.
Transnet on Thursday argued in the Labour Court that it had not been correctly informed about the planned secondary strike, due to start on Tuesday, and that it would be unduly affected if such a strike was allowed. It also warned that the strike could turn violent, based on the high levels of violence seen against non-striking truck drivers.
"Violence has become part and parcel of our industrial relations landscape," said advocate Puke Maserumule, acting for Transnet.
But Satawu hit back, saying the parastatal was using technical points, "strained readings" and an "11th-hour" appeal for a report from the Commission for Conciliation, Mediation and Arbitration (CCMA) to delay the secondary strike until it would be irrelevant.
"Neither Satawu nor its members has anything to gain from doing damage to Transnet or the economy," said Jason Brickhill, acting on behalf of the union. He also argued that the short duration of the planned strike made it less likely to be dangerous and the right to strike should not be limited because others had broken the law.
Satawu intends embarking on a one-day strike at Transnet's freight rail operation and a three-day strike at port operations. Importers and exporters have expressed alarm at the prospect, saying it would in effect halt all cross-border trade.
Transnet also raised concerns on Thursday, saying Satawu had already shown a willingness to ignore a collective bargaining agreement and that the intention was to "cause havoc at Transnet and do damage to the economy".
"It's a punitive secondary strike," said Maserumule. "We are big, we are vulnerable, therefore they strike."
He speculated that Satawu was becoming desperate because some workers in road transport have settled for increases below its demands. "[Satawu] is losing the battle because other employees in the sector are willing to accept terms … On its own it has very little prospect of being able to win the battle."
The better part of three hours of argument on Thursday afternoon centred on the nature of an agreement in place between the union and Transnet and whether Satawu had provided sufficient grounds for a strike in terms of that agreement. The courts could not allow unions to walk away from such agreements, Maserumule said, or encourage them to be broken.
Satawu painted the planned strike as a pure gesture of solidarity with the intention of increasing pressure on road freight employers, and raised no issues with Transnet itself. Such a strike would be entirely legal, it said. Halting port operations, for instance, would prevent companies using scab-labour drivers from doing business.
If the court agrees, it could allow for strikes in a number of other industries in support of the transport workers, including manufacturing, refining and agriculture.
On Friday morning, Judge Anton Steenkamp was due to rule on whether the strike may go ahead or be delayed to allow the CCMA to prepare a report.
Strikes of both the protected and wildcat variety have spread across South Africa over the past two months. As many as 100 000 workers are estimated to be on strike. The industrial action started on the platinum mines of North West, but has since spread to other mines as well as other industries.
It has been plagued by violence and a number of lives have been lost.
Several affected mines have suspended operations for varying periods of time.
Xstrata's communication and transformation manager, Christopher Tsatsawane, told the Mail & Guardian that on Thursday the "illegal industrial action" at its Eland platinum mine had turned violent and it would be shut down until after the weekend.
"This was done as a precautionary measure to protect lives and property," he said.
Also on Thursday, the Cabinet released a statement expressing its concern over "the lawlessness, violence and intimidation that continue to pollute the otherwise democratic right for workers to strike".
"It is a fact that, as a democracy, the right to strike is a defined right in South Africa that obligates the strikers to observe that they cannot encroach [on] other people's rights as they enjoy theirs," it said.
"No one should be intimidated to take or not to take [part in] an industrial action in a democracy. No one should resort to any form of violence against people or property as a form of striking or protests.
"Our struggle for freedom and democracy ensured that our laws provide a space for protected peaceful strikes, which obviates the need for illegal strikes accompanied by violence and intimidation," the Cabinet statement said.
It called on workers to use the existing channels with unions to address grievances and wage negotiations "in a manner that is in touch with our laws and collective bargaining practices".
It said that the illegal strikes and the accompanying violence were not "helping the country's image internationally".
Earlier on Thursday, President Jacob Zuma said he would be meeting all concerned parties on Friday to find solutions to the labour unrest in most sectors of the economy, according to Sapa.
Additional reporting by Lisa Steyn