ATHENS A movement more insidious than crippling strikes or anarchist fire bombings is threatening to undermine Greece's efforts to escape a debt crisis shaking the euro zone.
The "I don't pay" movement -- a sullen form of uncivil disobedience -- is beginning to starve the government of vital revenue from transport and public services as it struggles to plug a giant budget hole.
Fed up with wage cuts and tax hikes while corrupt politicians seen as responsible for the crisis enjoy impunity, more and more Greeks are refusing to pay for road tolls, bus tickets and other public charges.
"It's not easy to take to the streets holding a Molotov cocktail, but it's easy to say I won't pay," pollster Costas Panagopoulos said. "The 'I don't pay' movement is now the main risk for the government."
The ruling Socialists must show within months that tax evaders and those who profited from past corruption are being punished if they want to contain the movement, he said.
The political and legal system grants politicians almost blanket immunity from prosecution, and efforts to fight tax evasion have been slow to show results.
Despite tough austerity measures, social unrest has so far been more subdued than expected as the majority of Greeks have grudgingly accepted that some sacrifices are necessary.
But growing numbers of people are choosing to show their anger by refusing to pay for highways, public transport and state TV licence fees.
More than 56 percent of Greeks approve of this kind of protest compared to 39 percent who don't, according to an MRB poll published in a Sunday newspaper.
Launched as a fringe disobedience movement by residents living near the Afidnai toll gate on a main highway into Athens, the 'I don't pay' action group initially only dodged road tolls.
But it has gathered support from leftist groups and gained momentum since recent rises in public transport fares and now claims more than 10,000 registered members.
Its website denplirono.wordpress.com has more than 82,000 hits. The site calls on people not to validate tickets and offers instructions on how not to pay tolls -- politely asking collectors to lift the barrier.
"We want free roads," said Vassilis Papadopoulos, 59, an ophthalmologist who drives 60 km (38 miles) on a toll road every day but has not paid a single euro in the last year and a half.
"We are not willing to suffer the results of mismanagement, corruption and the crisis of a system we never chose," he said. "It would have cost me at least 2,000 euros a year only in toll fees to go to work."
Local communities have also opposed higher tolls, saying most of the roads are partially completed and offer poor services. In January, the mayor of the town of Stylida in central Greece had bulldozers remove barriers stopping locals from using a side road to avoid tolls.
Operators who raised tolls last year in line with concession contracts signed in 2007, say toll-dodging drivers jumped from about 6 percent to 15-18 percent in less than a year.
And it is not only tolls. In a bid to reform loss-making public transport and help plug its fiscal shortfall, the government also raised fares last month.
The price of a ticket valid for 90 minutes on urban transport jumped to 1.40 euros from 1 euro.
"1.40 euros a ticket? It's a 40 percent rise when all else went down -- wages, pensions, minimum benefits," said Maro Fassea, 48, an IT consultant, who joined hundreds of 'I don't pay' protesters outside parliament on Tuesday. "We've paid for our public transport and roads 100 times over through taxes."
Refusal to pay is threatening not only public finances but also an 8.7 billion euro (14.2 billion pound) road expansion programme that the recession-hit country badly needs to pull itself out of the crisis and attract new investment.
About 2.9 billion euros of state and private funds have poured into the toll roads so far, but operators say revenue losses could blow up the projects, already plagued by court wrangles and a suspension of bank funding.
"We are talking about 8,000 users a day who don't pay," said Fani Lambrou, spokeswoman for Nea Odos, a company which operates a 172 km highway in central Greece. This means minimum daily losses of 16,000 euros.
The rising movement has prompted Greek Prime Minister George Papandreou to warn that any road project cancellation would be a major blow to the country.
"If the contracts default, which is a possibility, our country's credibility will be damaged," he told parliament. "They will say that we do not honour our signature."
As it gains ground, the movement may also hurt government efforts to get people and businesses to pay their taxes, a crucial part of efforts to put finances back on track.
"The 'I won't pay' movement draws strength from the fact that the political system is unable to prosecute any of the corrupt politicians of the past decades," said Yanis Varoufakis, professor of economics at the University of Athens.
"The movement is likely to grow," he added. "As the crisis deepens, its momentum will be boosted and, as a result, the government's tax collection efforts will falter." (Editing by Dina Kyriakidou and Paul Taylor)