Any flying, sitting reserve, or any other airline duty will be removed from your line for military leave. It doesn't matter whether it's a drill weekend or a year long deployment, voluntary or involuntary. The airline likely won't pay you for any dropped time. I don't know of any airline that does, although some companies do. All companies, however, are required to accommodate your military schedule. I try to give my airline as much notice as possible, although I have had to drop short notice mil leave before (1 day notice). Bottom line, it's a pretty easy to do, but don't be "that guy" that abuses it.