Traffic was gridlocked in parts of Athens on Tuesday as transport workers joined a strike over planned pension reforms, while thousands marched peacefully through the city center demanding the draft law be scrapped.

With the subway, trains and public buses at a standstill, many commuters were forced to drive to work, leaving major traffic arteries into the sprawling city of almost 4 million blocked. Passenger ships remained docked at ports. Unions are also holding protests in Thessaloniki and other major cities.

The one-day stoppage was convened by public sector unions who are concerned the reforms will mean more cuts to pensions that have been progressively whittled away since Greece took its first financial bailout in 2010.

"I've been working since I was 17, and they are telling me I won't get a pension until 67. Will I endure this until then?" said Nectaria, 48, a single mother who works as a cleaner.

Others had little sympathy for the strikers. "A strike has never accomplished anything," said pensioner Dimitris Polychroniadis, angry that he had to pay for a taxi instead of taking public transport.

The new conservative government says the reform, to be voted on by Friday, will make the troubled Greek pension system viable to 2070.

The labor ministry says the overhaul, the third major revamp in a decade, will contain pension increases and reduce penalties for pensioners still working. Successive governments have attempted to reform the pension system, whose previously generous handouts are seen as one of the causes of the decade-long Greek debt crisis.

"The government will pay dearly for the further dismantling of social insurance, as (its predecessors) did. The Greek people do not forget," said Communist party General Secretary Dimitris Koutsoumbas.

A separate government bill to stiffen regulations on street protests is also causing anger among unions.

Chronic overspending and the inaccurate reporting of the budget deficit spooked creditors in 2010 and required three successive bailouts by the European Union and the International Monetary Fund to avert a Greek bankruptcy. In return for billions of euros in rescue funds, Greece had to adopt unpopular austerity reforms and pension cuts.