Well, a hijab isn't a problem, but a loose flowing abaya, in some fields, as pointed out by miss mimi, could be. that said, I know lots of muslim ladies who wear hijab and when needed will switch to a tighter fitting garmet: like when playing sports or doing certain work, they'll wear long pants and long sleeved shirts. they're still covered, but there's no extra fabric to get in the way.

In fact, back home, a friend of mine wore hijab. She was going for a job as a television reporter, in a predominantely non-muslim area, and at the interview said she'd be willing to adjust her dress accordingly: wearing shayla instead of hijab, if that was what was needed, or taking it off entirely to pursue her professional dreams. The station actually told her no, they wanted her to wear the hijab-- it represented diversity on camera and they liked that! So I think most people around the world respect it, as long as it doesn't hinder or change the quality of your work.

that said, I do think it's reasonable for a company to say you have x number of breaks a day: I know some muslims, here and back home, who take breaks for prayers, and breaks for coffee, and breaks for cigarrettes, and breaks for lunch, adn I start to wonder: when do they work? :P