When I was growing up in Catholic school, they told us that you couldn't give up work for Lent. I haven't checked with the Vatican to see if that's still true, but I just read a fascinating blog post, "Lent, Catholicism, Religious Accommodations", discussing the case law on accommodating Catholic employees' religous beliefs, particularly during Lent. A tip of the hat to
David Foley's Labor and Employment Law Blog