All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
You must be aware of the false principles that the Catholic Church is working to spread through these charity organizations; so working in them involves prohibitions, like helping in evil, or seeing it without denying it, or deceiving and misguiding the Muslim public.
Hence, you should not work for a Catholic charity. You should know that whoever leaves something for the sake of Allaah, Allaah will compensate him with something better. Allaah says (what means): {And whoever fears Allaah - He will make for him a way out. And will provide for him from where he does not expect.} [Quran 65:2-3]
Moreover, Imaam Ahmad reported from a Bedouin that he heard the Prophet saying: “You do not leave anything out of fear of Allaah, except that Allaah gives you what is better than it.”
Allaah Knows best.