Question for any FAA or legal gurus out there.

I work as part of a 2 pilot crew on a Lear 40 both 91 and 135 (management company for the owners)

The 135 company we operate under expects us to be on call 24/7 with no guaranteed days off.

Per 135, pilots are to receive 13 days off per quarter.

To meet this, company goes back and counts any day(s) we weren't assigned duty as days "off" regardless of the fact that we had been on call that day.

Something about this doesn't seem totally legal per FAA rest requirements.

Any thoughts or similar experiences?