The ruleset governing the faction wars, under which making deities act outside their nature counts as cheating.
Baroness Victory states the relevant clause plainly when Samantha accuses her of conspiracy: sponsors causing deities to act outside their nature is against faction wars rules because it gives an unfair advantage.
She adds the realist's caveat — that usually doesn't stop it from happening anyway, and there's only so much she can do about it — but it is considered cheating, and she reminded both the Maestro and the Rectrix of that before coming to observe Carl drop a bomb at his own feet. The other rule the chapter enforces is blunter: the boss battle isn't over until you get out of the club.
The governing framework Victory invokes over sponsor interference with gods.