Striking stevedores blocked trucks from entering Ports of Auckland in a bid to stop non-union workers unloading a container ship this morning.
Police were called at 7:15am after a group of about 100 picketers confronted truck drivers and non-union stevedores outside the port.
Trucks were backed up outside the port at about 7:40am.
Maritime Union president Garry Parsloe said the striking workers were trying to stop an NYK container ship being unloaded at Fergusson Terminal.
He said the ship, which was set to be unloaded by non-union stevedores who replaced striking workers, was part of the spreading "cancer" of the employment dispute.
The port had since told the union the ship would not be unloaded if they would allow cruise ships to berth, he said.
"It's all fixed at this time. We're only taking action against the ships that are taking action against us.
"We just don't want these ships in there and have non union workers doing our jobs while we're on strike.
It's reprehensible."
Police warned motorists of heavy congestion around the area where workers were picketing.
Inspector Cornel Kluessien said a contingent of officers would remain at the port all day.
Mr Parsloe said the disruptive action was "particularly important" as the union was set to meet with Mayor Len Brown today.
He hit out Ports of Auckland board chairman Richard Pearson for refusing to attend the mediation.
"If your boss called you into a meeting and you flat out refused to go you'd expect to be fired. We'll be asking why he's not there. We'll be asking the mayor what he's doing about it."
Mr Brown, a member of the Labour Party, who received a $2000 donation from the Maritime Union towards his 2010 election campaign.
On Friday, he was the target of a lamington attack at Auckland University by an angry supporter of wharf workers, who smeared pieces of cake on the mayor's face and shirt.
Yesterday, Mr Brown said Aucklanders simply wanted their port back to full capacity and he would try everything to bring about a solution, including an offer of mediation if both parties agreed.
Mr Brown said it would be wrong to interfere before last week when the two sides were still talking, but given the importance of the port to the Auckland economy he owed it to Aucklanders to explore all options. He reiterated the need for the port, which is 100 per cent owned by the council, to double its dividend from 6 per cent to 12 per cent within five years.
