Sortiarus

The Empire, like most nations around the world, has long had seers (called 'sortiarus' locally, for the popularity of divining fate by lots) who didn't conform to the type of magic employed by wizards. Only recently however, that form of magic has been outlawed by the Empire, along with all other forms of non-wizard magic except those gifts bestowed upon the Emperor's favorites. Black market services are still available of course, and most local fortune-tellers still run a brisk trade in the shadows, usually having plausible deniability (and a few thugs on standby ready to rough up the families of anyone who tries turning them in), though a handful have been executed in rather spectacular fashion.
Most wags assume that wizards acquired enough support in the Senate to have their competition eliminated, since wizards have always been either from prominent families or poised to create them. The number of senators with a Mark is rather surprising given the rarity of such a gift, and most others have wizards in their extended family at least. Surprisingly, wizards have little sway over laws, as their powers are greatly feared by the majority of the populace and the senate; appeasement is easy for senators, but they would never cede more power to wizards. No, the reason for the ban comes directly from the Emperor himself.
Rumors are that the Emperor is embroiled in a war that even he cannot win, and that the little gods of the entire world groan under his unnatural longevity and leadership. The very spirit world itself now bends against the Emperor if the cunning men and women in the world know what they're saying, and the Emperor remains concerned about the conduits through which these spirits speak. Insurrection hasn't been attempted in the Empire for over a century, and most people want a peaceful life so long as they have food on their tables and their families can grow to take over their lives in a few years. The Emperor has maintained peace for a long time, but what if the very world rebels against him? Will he be able to keep his populace safe then? The Emperor doesn't wish for fortune-tellers to find out.