So, I was running a session last weekend, and had this situation come up. The PCs crashed a cult ritual, and the cult leader had her audience under the effects on an enthrall spell.
The party cleric had the bright idea to cast an enthrall spell of her own, to sway the cult in her favor. It caught me off guard, so I wasn't sure how to adjudicate it.
At the table, I made a snap-judgement to keep the game moving and called for an opposed caster level check. But now I'm wondering what the actual correct ruling should have been.