Iron rule is a phrase often used to describe a strict and inflexible way of enforcing policies or laws. If you are looking for synonyms for this term, there are several you might consider. A rigid rule, strict policy, severe standard, unyielding guideline, or firm directive all convey a similar meaning. These phrases emphasize a sense of unbreakable rule, one that cannot be bent or altered regardless of the circumstances. Whether you are discussing government regulations, workplace procedures or personal conduct, all of these synonyms invoke a sense of unwavering authority, standing as a stern challenge for anyone who might wish to challenge them.