It is legal to have bible study at a private business--there is no "separation of church and business"--as long as1 Those who do not attend do not suffer some negative consequence demoted not promoted when they should otherwise have been worse shifts or jobs etc.2 Those who do not attend are not harassed for not attending3 Those who do attend do not receive benefits raises, bonuses, faster promotion, etc. then those who not.If 1 - 3 happen, this may be illegal religion-based employment discrimination, and you may have a legal claim grounds for a lawsuit or to bring a complaint to the EEOC or your state's equal/civil rights agency. But if they don't let the bible study and attendence thereat affect employment, it is legal.