Greece's co-ruling socialist PASOK party lost another deputy on Thursday over the Lagarde list affair, the third this week, ahead of a key vote on a tax bill on Friday which is a part of measures required by international lenders to release further aid to the debt-ridden country.

Lawmaker Christos Aidonis quit the socialists and turned independent, criticizing the current leader of the party Evangelos Venizelos for "seeking to distance himself of all political responsibilities regarding the managing of the Lagarde list."

With Aidonis' departure, PASOK remains with 24 MPs and the three-party coalition government is left with a 163-seat majority in the 300-member assembly. The assembly is due to vote on Friday on a tax bill which imposes more tax burdens on Greeks in order to slash deficits and exit the debt crisis.

On Monday, the coalition lost two deputies from the smaller Democratic Left party. They intended to vote for a parliamentary probe against Venizelos for his alleged role in the handling of the Lagarde list which names tax dodgers.

The parliament is expected to vote next week on the creation of a parliamentary committee to investigate whether Venizelos, his predecessor at the finance ministry George Papaconstantinou or former prime ministers George Papandreou and Lucas Papademos should be tried for the case.

A preliminary judicial probe showed that the list Christine Lagarde is said to have handed to Papaconstantinou in 2010 as France's finance minister had been tampered with, letting possible large-scale tax evaders off the hook.

Wide-spread tax evasion is regarded as a key cause behind the Greek crisis which has led to the decline of living standards of the average Greek household.