As a general rule, magic is considered something that belongs to the common people, to tradesmen and servants, and not to be practiced by the gentry or peerage. It's much like how you won't usually find a gentleman spending time working at a forge. Art, learning, sport, and the dalliances of high society are proper pursuits of the gentry, while the peerage is more likely to take part in politics. Both may of course fund business endeavors, but they're not encouraged to go take a direct hand in it unless it involves some kind of "exploration" or "adventure," and then it's only acceptable to go abroad maybe once or twice.
Anyway, magic used by the gentry is... Well, it's not the "done thing." Still, it's most likely to get one snubbed when it comes to invitations to dinner parties and such, not actually get in serious trouble. Though some will invite one specifically to have a party attraction -- a bit of "disreputableness" is always an interest.
That said, there are a handful of taboos that will really get you avoided if not possibly prosecuted. The worst is performing necromancy -- specifically, the binding of a soul into a corpse, creating a zombie.
The dominant religions of the day require the body to return to nature in its own course, to be buried and decay naturally, and one faces quite harsh punishments from the secular authorities for the unlawful defilement of a corpse. The raising of a zombie is punishable by death. If that was not enough, necromancy carries excessive social stigma, so that even the rumor of it upon a person is enough to harm his reputation immeasurably.
Some of the wealthy (and no known commoners) have won trials against them for necromancy, but not a one has been accepted back by polite society. Many leave the land for some far stretch of the empire after this, much impoverished from the cost of the lengthy trials and ostracized from former friends.
Not truly illegal but still rather unaccepted is the use of binds directly upon people. Those who lay claim to "reason" declare that the presence of a bind tattooed upon one is ugly, little better than markings made by savages to denote a tribal membership, and such things are beneath the modern, civilized person. Others will say how impractical it is, for a cut on the flesh could break a bind, and a scar would make it almost impossible to restore the bind. But the real reasons behind this prohibition are rooted deeply in superstition.
Look at it this way. Nobody knows why and how magic works, precisely, just what does work. Someone may know that doing this may do that, but the precise workings down to the smallest bits, as if magic was a machine to be tinkered with? Completely unknown. It's like how most medicines, natural and derived, are to most people -- you may know the precise amounts of laudanum to use to achieve a desired level of intoxication and pain relief, but have no clue how it works on the molecular level. All you know is that it works.
So, to continue, the superstitions... At its most basic, it is a fear that to accept a foreign spirit into one's own body, no matter the kind, will lead to loss of control and eventual possession by that spirit.
For example, a common bind worked into wineglasses is one that protects against substances severely poisonous to humans. If one was to pour poisoned wine into such a glass, the poison would seperate out of the solution and slough off onto the table, while the wine itself went straight into the glass. If such a bind was worked around a person's neck, so that poison would never go down their throat, it would still collect in their throat and they would have to cough it out. But they would also have a spirit bound into their body for the bind to work, centered close to where one's voice seems to issue forth.
The superstitious fear is thus: how will we know for certain whether the words spoken by the person are his own, or those of the spirit in his throat? If a bind was worked over a person's heart or on his forehead, would his body necessarily remain his own? Users of magic cannot say much either way -- they claim that the spirits are not intelligent, but how much do they really know? How wrong could they be?
Also connected into this prohibition is the fear that the use of binds on people is dangerously close to necromancy. If one is unwilling to have some magic done on their body while dead, what of while they are alive? Indeed, a bind worked upon a person while alive may end up trapping the soul within the body upon death, a greatly-feared torment from whence many believe comes incredible damage to their mortal soul. The risk, it is deemed, is not worth it. And any willing to take that risk upon themselves are fools at best. Those who would put others to that risk are quite near to monstrous.