Forcing someone to actively practice a religion is probably illegal, but requiring someone to be knowledgeable in the religions practices even if it requires training, probably isn't[.]
"Be careful to do everything I have said to you. Do not invoke the names of other gods; do not let them be heard on your lips." (Exodus 23:13)
I have encountered people who take this very seriously; they will not say the names of the months or the days of the week. (Some old Quakers were like this too; they have "First Day School", and on old tombstones at the local Meetinghouse the dates are like "4th Month 23, 1782" -- they don't use the names of the months.)
SO, if these Scientology classes even require saying the names of deities, they have already gone over the limit of denying another person's free exercise of his religion.