the.com/iron boot

means A heavy, crushing form of control or punishment — a metaphor for oppressive force applied without room for argument.

from Draws on two real strands: the medieval torture device sometimes called the 'iron boot' or 'boot,' which crushed the foot or leg to extract confessions, and the long-standing figurative use of 'iron' for anything harsh, unyielding, or forcibly imposed (as in 'iron fist' or 'iron rule'). The phrase fuses the literal instrument of coercion with the metaphorical language of domination that English has used for centuries.