The government spokesman arrived at the venue in his own car, and after word got around that he was in the KAPI building protestors arrived and closed off the building, shouting slogans against the government and Memorandum, while a few demonstrators threw objects.
No one was hurt in the incident.
Petalotis delivered his address to the event as scheduled, while a team of MAT riot police kept the crowd gathered outside at a distance.
PASOK on Friday morning strongly condemned the incident, and accused cadres of the Coalition of the Radical Left (SYRIZA parliamentary alliance) as being the 'protagonists'.
"The threat of violence and jeering is condemnable, especially when the aim is to cancel a scheduled event by a political party. Also unacceptable is the effort of certain quarters to manipulate and exploit the peaceful protest demonstrations by the citizens for their own petty party benefits," an announcement by the PASOK press office said, and called on the political parties to "take a clear stance" on the incident which, it said, was against democratic dialogue and democracy itself.
"It is the duty of all the democratic citizens to safeguard democracy, the institutions and the free expression of every citizen, which generations of Greeks fought for," PASOK said.
Earlier, reacting to statements by Petalotis at the Argyroupolis event, SYRIZA said that the government spokesman attacking SYRIZA "is not news".
"We wish to point out, however, the orchestrated effort of the PASOK system to create a climate of defamation against the spontaneous mobilizations of the indignant citizens by attributing the mobilizations to inciters. It seems (PASOK) that they have not understood anything. The tide does not turn back. The overwhelming majority of our society seeks that the new measures do not come to pass, it demands that the government steps down," a SYRIZA announcement said.