Giorgos Bartzokas' team lost out to Panathinaikos in last season's domestic playoff finals after game three was stopped and later abandoned due to crowd trouble.
Having taken a 2-0 lead in the best-of-five series, Panathinaikos were leading the match 76-72 with 1 minute 27 seconds to play when fans invaded the court and showered Panathinaikos players and officials with missiles and flares.
ESAKE, the Greek top flight organisers, announced on their website Olympiakos were fined a total of 27,800 euros (£23,900) for "violence inside the stadium, the throwing of objects endangering the safety of players, referees and officials, and making it impossible to continue the match".
The heavy punishment had been fully expected as Olympiakos had previously received a six-match supporter ban for a similar offence in the playoff finals two years ago when Panathinaikos again clinched the title in Piraeus.
Greek sport has been plagued by fan violence during the country's economic woes.