This is why there are laws in developed countries to protect people from this hypothetical situation.
The merits of trade unions do not stop at strike action. This isn't the only thing unions provide. They employ many methods, strike action really is a last resort, you know?
*Negotiation
*Collective bargaining
*Work-to-rule
*Overtime ban
*Court cases
*Etc
Even direct action is not always necessary. More often than not, employers are reasonable and will negotiate to find a mutual settlement. Compromise is what makes the world work.
We work to find a peaceful settlement before taking to the picket lines.