ATHENS, Jan 10 (Reuters) - A Greek Socialist lawmaker resigned on Thursday from the co-ruling PASOK party after he criticised the government's handling of a list of possible tax cheats, further reducing the fragile coalition's majority in parliament.
Christos Aidonis, 50, a former deputy health minister, is the third lawmaker the ruling coalition has lost in less than a week over a deepening scandal that has outraged Greeks and tested the cohesion of the government.
Austerity-weary Greeks are angry that successive governments did little to pursue those on the list and Prime Minister Antonis Samaras is under pressure to back an investigation into his own coalition partner and PASOK leader, Evangelos Venizelos, over the affair.
"I'm leaving PASOK's parliamentary group and becoming independent," Aidonis said in a letter sent to the parliament speaker. "PASOK and the three-party government cannot operate as a shield protecting politicians who handled the list from being investigated."
Samaras's three-party coalition is now left with 163 lawmakers in the 300-seat parliament.
Aidonis, the ninth deputy to leave PASOK since national elections in June, said he would continue to back the three-party government.
His departure comes after the smallest party in the government, the Democratic Left, expelled two lawmakers on Monday for backing a probe into Venizelos.
The coalition has rebuffed calls for an investigation into Venizelos, who was given the list when he became finance minister in 2011. It only supports a probe into Venizelos's predecessor in the post, George Papaconstantinou, after prosecutors found names of his relatives were deleted from the list.
Parliament is expected to vote as early as next week on whether to investigate Papaconstantinou and Venizelos as well as two former prime ministers over their handling of the list.
The Lagarde list, which has more than 2,000 names, was first given to Athens by the French government in 2010, but little was heard of it until its existence was revealed in September last year. (Reporting by Renee Maltezou, Writing by Deepa Babington, Editing by Angus MacSwan)