Literally they will if tech workers unionize, which has its own baggage and list of disadvantages for everyone but if tech companies get in a bad habit of treating employees poorly that’s exactly what will happen.
No! A union explicitly means a random employee will lose the ability to add or remove any clause from their contract as the Union will negotiate that. That doesn't mean the Union wouldn't negotiate a better contract then the employee would on their own but you absolutely lose that power in almost all Union setups.
And also, unions don't exist to give workers the ability to stick arbitrary clauses in employment contracts, they exist to try to lobby for better standard terms for union members. And relocation packages for new employees are a very long way down a union members' list of concerns, since people tend to join the union after they've relocated...