In the USA Hockey Annual Guide the following paragraph outlines the requirement.

All ice hockey coaches and instructors of registered USA Hockey Youth 18 & Under and below, high school, girls’/women’s 19 & under and below, and disabled programs must properly wear an approved ice hockey helmet during all on-ice sessions, including practices, controlled scrimmages and all Coaching Education Program clinics and/ or workshops. Failure to comply will result in a 30 day suspension from all activities involving USA Hockey registered programs.