Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Council in Trullo; Often Called The Quinisext Council.: Canon XXXIV

Canon XXXIV.

But in future, since the priestly canon openly sets this forth, that the crime of conspiracy or secret society is forbidden by external laws, but much more ought it to be prohibited in the Church; we also hasten to observe that if any clerics or monks are found either conspiring or entering secret societies, or devising anything against bishops or clergymen, they shall be altogether deprived of their rank.

Notes.

Ancient Epitome of Canon XXXIV.

If clerics or monks enter into conspiracies or fraternities, or plots against the bishop or their fellow clerics, they shall be cast out of their grade.

This is but a renewal of Canon xviij. of Chalcedon, which see with the notes.