People attending Saturday night's Vivid festival have been told to avoid ferries amid concerns industrial action will bring further chaos to services already running at capacity.
The annual festival brought 270,000 people into the city centre last weekend and there are fears the decision by ferry workers to refuse to sell or collect tickets, or help with extra services organised for the event, will add to the chaos.
"Ferries are going to be operating at capacity and due to the industrial action passengers may experience further disruptions and be unable to purchase a ticket," a Transport Management Centre spokesman said.
"Passengers should avoid ferries and take advantage of extra buses and trains for the event."
The festival is one of the busiest times of the year for Sydney ferries, and workers will not sell or take tickets on Saturday and Sunday between 6pm and 10pm on all Sydney services. Manly ferries will take industrial action between 6pm and 3am.
Workers will also refuse to assist on extra chartered services arranged to deal with the huge crowds and will not switch on the lights on Vivid ferry services between 7pm and 7.30pm.
Maritime Union of Australia assistant branch secretary Paul Garrett said negotiators had made themselves available this weekend to resolve the lengthy pay dispute between the union, the Australian Institute of Marine and Power Engineers and private operator Harbour City Ferries.
Mr Garrett said services would be free for passengers and dismissed concerns about overcrowding, saying they would run as normal.
“Our fight's not with the public, our argument's with the company,” Mr Garrett said.
“Crowd control has been done at the highest of levels. I'm not aware of any disruptions,” he said.
Harbour City Ferries chief executive Steffen Faurby said extra staff had been put in place to cope with the crowds. He did however apologise in advance for "any inconvenience that anyone might experience".
Transport Minister Gladys Berejiklian said she was ''absolutely dismayed'' by the industrial action which would ''disrupt the journeys of so many people''.
"We are very keen to make sure everyone hears the message loud and clear before heading into town tonight. Take public transport and use buses or trains,'' Ms Berejiklian said.
''Ferries will be full, so we are being very clear - avoid using the ferry to travel into or out of the Sydney CBD tonight.''