[nbabitskiy]

Religious practice was certainly illegal, unless it was official Orthodox, Muslim, Jewish etc. There was no way to organize a non-canonical congregation, unless it was a clandestine operation for a dozen people.

There was an article in the RSFSR Felony codex ("breaking the laws of separation of the church from the state, and of the school from the church", #142) the sole purpose of which was to outlaw religious congregations.

Many baptists (mostly Ukrainian) were imprisoned indefinitely - well into eighties - for refusing to obtain passports.

Finally the idea of "legality" of something for which you get persecuted and mocked by state and party officials (as part of their line of duty), and get auto-fired from a significant part of the economy in a state with no (legal) private economy seems a little twisted.

[Koshkin]

Well, it is not unusual when some religious practices turn out to be incompatible with law.

[ddsea]

The repressions varied in time, place and also depended on who's in charge. As the old anecdote goes, bent along the line of the Communist Party.