The full process of labor contract negotiations between a unionized workforce and the company is long, complicated, and would include a strike/lock-out near the end.

Airline unions are governed by the RLA (railway labor act) which was intended to make it harder for transportation workers to strike and inconvenience the travelling public. The government gets more involved along the way, and the process can drag out forever (if management wants it to).

In this case it sounds like the union and company cannot agree on anything in their own discussions (big surprise there), so The National Mediation Board (NMB) will now conduct mediated discussions. The NMB will act as a marriage counselor and try to bring the two parties closer together. This will probably not work either.