The True Light is the secret underground religious organization of the Empire. It is secretly followed by thousands, if not hundreds of thousands of people who seek to bring comfort to their lives. Unlike the Imperial Church, the True Light Movement has no true single leader. They devote themselves to the purity of the light.
Practitioners of the True Light are able to empower themselves far better and with far greater strength than the Paladins of the Imperial Army. Thus its presence in the Empire is indeed a significant threat to the Imperial Order.
The Emperor's Loyalty Guards and Loyalty Ministers are always on the lookout for those who practice the True Light. Anyone found is immediately arrested with no need of warrants. They can be convicted without trials.