I work in a hotel, and as such, we are open 24/7/365. I informed my boss when I was hired(2days ago) that I am a practicing Catholic and I can't work sundays and holy days. In practice though, he doesn't always let people off for such things. is it a sin if i have to work on a holy day of obligation? I am worrying!
The following links should help answer your question about working on Sunday. If you have any further questions, please contact Catholic Answers directly.