Are you asking if sorcery is illegal in Westeros? Then the answer is no, for the most part. There’s plenty of examples of people using the services of maegis of various stripes, from Targaryen kings down to Lannisport smallfolk.

However, it does seem as if sorcery is fairly taboo in Westeros, as we can see the Faith of the Seven being pretty consistent in their opposition to sorcery, as we can see in the case of street preachers condemning Bloodraven or the High Septon pleading with Aegon V not go through with his ritual at Summerhall, or (and this is the closest we get to illegality) Baelor I burning the writings of Septon Barth for his heretical investigations into sorcery.