Let’s say some people at a company want to get together during lunch hour and hold a Bible study. It’s totally voluntary, and they don’t pressure anyone else to attend. This is not likely to cause any problems.
But let’s say the boss organized the Bible study and attends it regularly. Now we might have a problem if subordinates are coerced to attend overtly or even subtly. (If, for example, those who attend get in good with the boss and are first in line for promotions, raises, etc.)