your, his, etc. word is law

(one's) word is law

One has the ultimate authority; you must do what one says. You better do it, or you know what'll happen. Mom's word is law. I don't care what your supervisor said. I'm the boss here, so my word is law.
See also: law, word
Farlex Dictionary of Idioms.

your, his, etc. ˌword is ˈlaw

used to say that somebody has complete power and control: Their father is very old-fashioned. His word is law in their house.
See also: law, word
Farlex Partner Idioms Dictionary
See also:
  • drive (one) out of office
  • force (one) out of office
  • force out of office
  • give (one) (one's) head
  • give head
  • give somebody their head
  • give someone their head
  • cooking for one
  • as one door closes, another (one) opens
  • as one door closes, another opens