Greek lawmakers ratified on Thursday afternoon a bill on the country's pension system reform, as public sector services were once again disrupted by a four-hour nationwide work stoppage of civil servants who denounce the change.

The bill, which introduces the end to widespread early retirement and increases the minimum age of retirement to 65 years, was approved by a 156-128 vote in the 300-strong parliament. Not all deputies were present.

The vote took place as dozens of international and domestic flights were canceled and thousands of civil servants staged a walkout from their posts and held rallies in Athens and other cities protesting against the reform.

The bill was slightly changed on Wednesday, as even deputies of the ruling socialist PASOK party raised objections. PASOK has a majority of 157 seats in the current parliament, since three deputies were expelled from its parliamentary group two months ago, when they voted against another crucial bill on the austerity measures.

The Greek government presented the bill as a necessary step to tackle a severe debt crisis that hit Greece in late 2009 and has alarmed European partners and markets.

The government claims that without a drastic and painful reform of the social security and pension system this year, the whole system could collapse in the next decade.

But Greek employees in the public as well as the private sector reply that they simply cannot survive with such changes, and suggest the government seek the money to pay debts and overcome the economic crisis from tax evaders and corrupted officials and businessmen.

Hundreds of protesters gathered in front of the parliament in the center of Athens on Thursday noon, chanting slogans against the bill and staging a short theatrical performance.

It depicted the "suffering and death" of the public servant who is constantly hit by harsh measures implemented by the government, the European Union and the International Monetary Fund (IMF).

Greek protesters blame the EU and the IMF as well for the policies, since the activation of a support mechanism for Greece last May. European partners and the IMF agreed to financially help Athens with a 110-billion-euro (140 billion U.S. dollars) package over a three-year period, if Greece proceeds to harsh changes without delays.

Thursday's mobilization was organized by the umbrella labor union of public sector employees ADEDY, which along with the main labor union of private sector employees GSEE has staged seven general strikes in the country so far this year and warned with more over the austerity measures.