Yes, it's a crap situation. Not knowing what their contracts said, though, this is perfectly legal for Disney to do.
That being said, Unions are a great way to ensure stable employment, especially in the entertainment industry. Ask me how I know (20+ years of doing this stuff as a technician and an IATSE member). THAT being said, Unions aren't perfect and Actors Equity most certainly plays favorites on what contracts they give a crap about. AFAIK, Disney works with AEA and non-union for performers and their contracts demand only a certain percentage of performers be AEA members. Really what this boils down to is, if you ain't in the club, you ain't gettin' respect.
I feel for the performers, but after decades of navigating this business I can only sit back and think about how this is a wonderful learning opportunity for those involved.