He is the second ruling party MP to resign on Thursday, and the third in less than 48 hours.
Briefing Parliament on his intention, Nassiokas said that "this is the least I can do to reverse today's condition of impasse, for the salvation of the country".
Nassiokas did not express intentions of declaring himself an independent.
Speaking minutes after the Larissa-area MP and former minister's resignation, former Parliament president and high-ranking PASOK deputy Apostolos Kaklamanis noted that "we do not serve our country by resigning. We serve it here (in Parliament), where the people sent us."
Almost simultaneously, former PASOK minister Vasso Papandreou and other MPs called for the immediate convening of the ruling party's Parliamentary group, a request which is expected to materialise at 4:30 p.m. (14.30 GMT).