Greek lawmaker Christos Pappas was the latest supporter of the far-right Golden Dawn party to face charges of belonging to a criminal organisation.
He was arrested on Sunday after handing himself in.
He appeared the same day before a prosecutor and an investigating magistrate.
The party's leader will appear in court on Tuesday to enter his pleas on the same charges.
A party spokesman, four other lawmakers and 13 party members are due to enter pleas on Wednesday.
It's the biggest mass detention of legislators since the end of Greece's military dictatorship almost 40 years ago.
The party was investigated after the fatal stabbing of an anti-fascist rapper earlier in September.
Investigators were looking for evidence linking it to that and a series of other criminal offences.
The party denies any connection to the killing.
The inquiry has also led to a shake-up among Greek police after the discovery of Golden Dawn cells operating within