If they tried to take action against anyone for allowing a United jumpseater than they are opening themselves up for a failure to represent lawsuit.
A very interesting point that I had not considered.
When it comes to hiring, pilots have a long memory, especially when one is attacking their pilot group.
Unbelievably long. The United strike was in 1985. The Continental strike was in 1983. There are probably 250ish people still at United that crossed the picket line at one of those strikes. Most pilots will not speak to them outside of good CRM. Once at the layover hotel, they are not welcome to join the crew if they go out for dinner/socializing.
20 years ago, their treatment was much harsher. Remember those metal "clickers" kids have that would make a loud clicking sound? Back then, when someone who crossed walked in to Ops, everyone carried them and would start clicking them until it became such a cacophony that the person would leave Ops.
I can't imagine how harsh it was in the first 5 years after the strikes.
Except cases required by FAR (FAA inspectors for example) it is the Captains right to allow or not allow it to be used and by whom.
And if you crossed a picket line, expect that you will not be given a jumpseat by an ALPA Captain. Even if the plane is empty.
Finding out who crossed any and every unionized airline picket line is pretty easy. Just google "ALPA Pilot Scab List".