More than 100 wharf workers have gone on strike at Fremantle Port and the Kwinana bulk terminal, south of Perth.
The Maritime Union says members have stopped work because they want their new enterprise agreements to include a clause guaranteeing they will not lose their jobs if some or all port operations are privatised in the future.
The union's Will Tracey says the Transport Minister Troy Buswell has promised that will not happen but the workers want it in writing.
"We're keen to get these guys back to work and get this port working as soon as we can," Mr Tracey said.
"The Government's just got to come to a commonsense decision." Mr Tracey says the industrial action is a last-ditch effort to get job security.
"We just don't want to see a situation where either privatisation or asset sales is used to manufacture mass sackings without any involvement or consultation with the union," he said.
"That's the concern we've got." On the weekend, Mr Buswell ruled out privatisation of the port.
"The Government has absolutely no plans to privatise Fremantle Port," he said.
"It's a state-owned port and as far as we're concerned always will be a state-owned port." Offer The Fremantle Ports CEO, Chris Leatt-Heyter, has told the ABC the workers have been given a fair and reasonable offer.
"The issue that they've got is they want security of employment," he said.
"From our perspective, that's not a reasonable or an appropriate term.
"We need to be able to run our business in the way that's proper." Mr Tracey says the stance is disappointing.
"The Port appears to be saying that we want the right, if we seek fit, to be able to dismiss longstanding employees from the port and that's disappointing from our point of view," he said.
The union and the Port were in mediation discussions at Fair Work Australia for four hours today but the dispute was not resolved.
The Fair Work Commissioner, Danny Clogan, told the parties to reflect on their positions, and said he was not prepared to let the matter drift and just let the law of the jungle apply.
The parties were ordered to resume talks tonight but if there is no agreement, the dispute could last until Christmas Eve.