That's how it works in other countries. Unions are per industry, not per business, because per business is... weird and not really helpful.

The union negotiates salary ranges for the entire industry, so it doesn't matter if one company is being difficult, their organisation (the one that organises the employers of that industry) have agreed to the ranges on their behalf.

If you need to go on strike, the union members employed at other businesses can help cover wages. Your union can also call for sympathy strikes at other businesses, putting additional pressure on the misbehaving company.