Hold somebody to ransom
Definition 1 of 2
Pro Tip 1/3Literal Usage
Originally, it refers to kidnappers demanding payment for the release of someone they've captured. 
In movies, criminals often hold someone to ransom until their demands are met.
Pro Tip 2/3Metaphorical Sense
It's used metaphorically to describe any situation where someone is forced into a choice by severe threats. 
The employees felt held to ransom by the threat of layoffs.
Pro Tip 3/3Negative Connotation
The phrase often implies an unfair or immoral power imbalance. 
The software company was accused of holding its clients to ransom with expensive updates.