General fasts had been previously observed by the Israelites (e. g. Judges 20:26; 1 Samuel 7:6); but we do not hear of any fast having been “proclaimed” by authority before this.
Related Commentaries of 2 Chronicles 20:3
2 Chronicles 20:3
3 And Jehoshaphat feared, and set himselfa to seek the LORD, and proclaimed a fast throughout all Judah.