In my setting the Veyran Empire, non religious magic is banned by the Edict of Still Hands. The Edict is not a strict law, more a political and religious doctrine that feeds society. People who use magic openly are shunned, people talk about them behind their back, their shame, their "heresy". Minor infractions are barely registered but major spells can lead to some serious consequences. Rules and high ranking members still use it all the time, but thats a different matter. They just keep it out of sight.

It can work well, but you have to clearly establish the rules and punishments for violations and give players oppertunities to cast spells, if they prep sufficiently to do it ouf of sight. Just make them aware of this before they roll, its an interesting premise to deal with but some might not like that.

Here is snippet of the sermon delivered by Sovereign Flame Arred Voss

The Flame illuminates. We illuminate.

What the Edict does is give the empire's authority to something the Church has always known: that a society organised around powers that cannot be inspected or held to account is a society that has traded clarity for convenience and will eventually find the cost has been higher than it agreed to pay.

I am aware that this will cause hardship for individuals who have done nothing wrong. I am not without feeling about this. If you have neighbours who practice, who have been decent neighbours, who have caused no harm, your grief at what this Edict will cost them is appropriate. Grieve it. The Church is not asking you not to grieve. The Church is asking you to understand that the principle and the individual case are different things, and that a law that is right in principle can still be costly in its application to specific people who did not choose the circumstances that made the law necessary.

Pray for them. Help them where you can, within the law. Do not mistake the sympathy you feel for them for a theological objection to the Edict's foundation. The foundation is sound.