Spellcaster Curse (3.5e Feat)
From D&D Wiki
Spellcaster Curse [Hex]
Your Hexblade's Curse hampers enemy spellcasting.
Enemy spellcasters who are affected by your Hexblade's Curse suffer the penalty imposed by your curse (-2/-4/-6) to their spellcaster level and the save DC of their spells and spell-like abilities. This penalty is only applied to spells cast while under the curse, not already active spells. Supernatural and other abilities are unaffected.
A hexblade may select Hex Spellcaster as one of his bonus feats.
As per magic-psionic transparency, this feat also hampers the manifestation of psionic powers and psi-like abilities, but not supernatural abilities that mimic psionic powers.