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 the port's operator Fremantle Ports is refusing to guarantee there will be no forced redundancies if 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.
"If they commit to going to the independent umpire, we'll pull this action off," he said.
"We're keen to get these guys back to work and get this port working as soon as we can, the Government's just got to come to a commonsense decision." The workers 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.
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." The union has set up picket lines at Victoria Quay and Kwinana.
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 Leatt-Heyter says the action has not had an impact yet but may affect container ships this afternoon.
On the weekend, Mr Buswell categorically ruled out privatisation of the port.
"That is a ridiculous claim, now 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." Mr Buswell went on to say that negotiations have been frustrating.
"They are incredibly difficult to deal with," he said.
"Our response to them is keep the port open, accept a very generous pay rise and understand very clearly the fact, and that being that Fremantle Port is not and will not be privatised." Mr Tracey says members, who remain concerned about privatisation of services, had been hoping to avoid a Christmas strike.
"We've agreed to take all action off the table if the parties are prepared to put the matters before Fair Work, let them decide and see if the concerns of the port and the government are valid," he said.
"We'll take all this action off and get these vessels moving prior to Christmas." Fremantle Ports says it is concerned by the stoppage which could affect container and grain shipments.
It says such action at this time of year will be a severe blow to importers, exporters and the wider community.
The parties are currently meeting to discuss the issues.