dictatorial (as in insisting on precise compliance with rules, esp., though not exclusively, when it comes to matters of grammar) adj. prescriptive

[A person who has this mindset is a prescriptivist. The opposite, a descriptivist, is also described here.] Grammar prescriptivists love rules. These are the self-described grammar Nazis, or the grammar police, who make it their life’s undertaking to ensure that every grammatical rule is followed all the time. These are the people who cringe when someone uses the word “literally” incorrectly. Grammar descriptivists, on the other hand, started playing fast and loose with the word “like” way before Clueless was in theaters. (https://thewritepractice.com/prescriptivist-descriptivist)

This word, when used in the above sense can also be a synonym for authoritarian, autocratic and oppressive.