Former Prime Minister Alexis Tsipras accused Prime Minister Kyriakos Mitsotakis of presiding over a wave of corruption.
He said the government is now sacrificing officials to save itself as scandals pile up ahead of elections due in 2027.
"While the boat is sinking from corruption, Mr. Mitsotakis is throwing the ballast overboard to save himself," Mr. Tsipras told Best TV in the southern city of Kalamata. He called the prime minister the "high priest of corruption."
He said Greece had never been a bigger "client" of the European Public Prosecutor's Office, which investigates fraud involving EU funds.
Mr. Tsipras focused on the Independent Authority for Public Revenue, Greece's tax agency.
He said Mr. Mitsotakis kept its head, George Pitsilis, in office for a third term, although the law allowed only two.
He said the agency ignored warnings about tax evasion by the Choriatiko bakery chain, whose owner was jailed last week in a case of alleged tax fraud worth more than 100 million euros.
Mr. Tsipras cited media reports that 25 agency officials had taken bribes from the company.
He also questioned the government's decision to give the tax agency control of OPEKEPE, the farm subsidy agency at the center of a major fraud scandal.
Mr. Tsipras now leads the Greek Left Coalition, which is second in opinion polls behind Mr. Mitsotakis' New Democracy.