lay down the law

verb3

1. •
   To promulgate law.

   • Six or eight thousand years ago / They laid down the law / In Mesopotamia — 1982
2. •
   To authoritatively or dogmatically assert what is permitted or not permitted.

   • He concluded this sentence with a self-important cough, as one who has laid down the law in an indisputable manner. — 1818
3. •
   (old-fashioned) To present the law that applies to a given case.