lay down the law

/L EY1 D AW0 N DH AH0 L AO0/
verb
  1. 1

    To promulgate law.

  2. 2

    To present the law that applies to a given case.

  3. 3

    To authoritatively or dogmatically assert what is permitted or not permitted.

Source: https://en.wiktionary.org/wiki/lay%20down%20the%20law