At my airline, they want military leave identified prior to the bid. They then pre-assign it (like vacation or training) and your schedule is built around it.

They give us 2.5 hours of "virtual credit" for each military day...this counts for scheduling but not for actual pay credit. I take 6 mil days in a normal month so my line award is reduced by 15 credit hours. I kind of like it, otherwise I would be working a full schedule in addition to drilling.

If you really didn't want to get penalized, you could just bid days off for military. You would need enough seniority to get the days you want though. If you did not get a day off when needed you could always drop mil leave after the bid, in which case they would pull you off the trip (possibly at an inconvenient stopping point).