Most teachers work in public schools so even if the principal could give them a raise they wouldn't be able to but in private schools they absolutely could.
Pilots are an interesting example because AFIK they negotiated terribly, i.e. they have all sorts of benefits and high salaries for the high-tenured pilots but new pilots are almost working for free. Student pilots have been told for years that there's an upcoming shortage of pilots but right now you're lucky to get a job anywhere in the world.
If you're looking for examples then look at europe. In my country everyone has the right to negotiate their salary once a year even though most people are part of a union. Where I worked I would always be able to get a couple of % added to my salary.
