This honestly sounds more like a cartel than a union.
The world is different now. Economy is global, people are trying to make a living doing something that makes them happy. Not everyone is a union member, and it’s absolutely ridiculous to extort a young professional from taking a career defining opportunity because a certain, very entitled group decides they want it even better.
Unions striking is within their right. Go for it. But it’s absolutely unacceptable to start blacklisting non-union people who don’t fall in line because the union doesn’t happen to have as much bargaining power as they would have liked.