One of the accused, Kannan N Balakrishnan, 47, was charged at the Penang Hospital where he has been warded for an injury.
The others were charged before Sessions Court judge Norsalha Hamzah under Section 130V (1) of the Penal Code for being a member of an organised criminal group.
The 20 accused are Ragindran Sivasamy, Pavithren Selvarajoo, Muneesparan Pawadai, Gunaseelan Subramaniam, Manivenam Subramaniam, Luke Stevenson Lourdesamy, George Sabastian Silvam, Gogulan Nair Kannan, Devathirran Gunasegaran, David Charles Anthony Dass, Selvarahoo Ganasan, Prabakaran Gangatharan, Murali Karuppiah, Thanimalai Subramaniam, Thinagaraju Gandhi Thaver, Jeegendran Ramasamy, Balakrishnan R Mutusamy, Vimaleshwar Ealelarasan, Somasundram Subramaniam and a 17-year-old boy.
No pleas were recorded and they were detained under the Security Offences (Special Measures) Act (Sosma) 2012.
The men, aged from 17 to 57, were accused of being members of an organised crime group in the Northeast District in Penang between Jan 1, 2015 and July 29 this year.
Saiful Edris Zainuddin and Muhammad Fadzlan Mohd Noor prosecuted.
RSN Rayer, M Athimulan, V Parthipan and A Asyok represented 12 of the accused at the court while the others were unrepresented.
Justice Norsalha fixed Sept 14 for mention.