US Airways management has decided to charge its affiliate Express carriers (not its owned airlines) $20 to non-rev. This is industry standard between airlines and contract affiliates, previously they were given a full term pass like actual US Airways and owned US Airways Express employees have.
As the turtle ponted out, some of these employees, particularly express flight attendants who cant jumpseat, may quit as the free travel was the only perk, or possibly they commuted and are now unable to do so (remember these positions pay the equivalent of minimum wage).
One of the carriers, Shuttle America, has paid a special fee to US so the employees still travel for free, I guess Shuttle America pays the fee for them. They are a very small company, I don't see this happening at a place like Mesa. This could be a reason for shortage of crews on top of the usual rapid turnover.