Dozens of ships will be stranded in Greek ports when seamen strike tomorrow against a government decision to lift restrictions on vessels with foreign crews docking in Greece, union and state officials said.

Passenger ships will be most affected by the strike starting at 3am on Monday, with at least 30 ferries not operating from Greece’s main port Piraeus, near Athens, and more across the many Greek islands.

At least five cruise ships were expected in Piraeus, officials said, and may be prevented from leaving or disembarking passengers due to protests.

In the first strike against the government’s move in April, protesting seamen prevented 870 mainly Spanish passengers on a Maltese-flagged cruise ship, the Zenith, from embarking or disembarking.

After seamen announced similar plans for tomorrow, the ship’s owners said the Zenith, with 1,000 passengers aboard, would not arrive at Piraeus, but would instead sail to Malta.

“Zenith is being targeted and has suffered losses. We’ll not risk going through the same again,” said Markos Nomikos, head of Donomis, the company representing the owners in Greece.

“If this situation continues, Zenith will not travel to Greece. Why is this happening? We don’t have any problems in Italy or Spain,” he said.

Greece’s Socialist government said in April that the Mediterranean country would allow non-EU-flagged ships with non-Greek crew to moor at its ports and travel between Greek islands, in order to boost tourism.

The move was seen as a first step towards liberalising Greece’s labour market and boosting competitiveness. The government, fighting a debt crisis that has rocked Europe, has stirred angry protests by embracing austerity measures.

Shipping companies were previously restricted to hiring Greek crews, and even EU-flagged ships did so in practice to avoid protests and labour stoppages.

“We are protesting against the government’s policies. We have to protect our rights and our jobs,” said Yannis Halas, general secretary of the Panhellenic Seamen Federation.

“It’s not a protest against tourist arrivals in Greece, but they can’t throw Greek seamen into the streets. They are also offering a lot to the economy,” he said.

Tourism is the top contributor to Greece’s €240 billion economy, accounting for about 18 per cent of GDP, while shipping is usually the second or third biggest, with five per cent of GDP.

Greece is the only country in the EU that imposes crew restrictions on shipping companies known as “cabotage rules”, the Economy Ministry has said.