According to the point I/14, the Ministry of Health decrees in line with § 2 paragraph 2e) act no. 94/2001 Coll. following conditions of the Right of Peaceful Assembly according to the act no. 84/1990 Coll. as amended:

1. any assembly organized outside of the building interior is limited to 20 participants retaining at least 2m distancing,
2. any participant of assembly organized inside of building interior is obliged to retain at least 1.5m distancing and disinfect his or her hands before the entrance.

Complete decree with the justification can be found here (in Czech).