NFL referees were instructed to penalize teams if coaches or others on the sideline approach them without face masks in place in a league memo unveiled Friday.
Such a move could produce a 15-yard unsportsmanlike conduct penalty against the offending coach's club.
"We have reminded game officials that if an individual not wearing a face covering approaches them inappropriately, they have the authority to take administrative or officiating action, including a 15-yard penalty for unsportsmanlike conduct," the memo said.
A posting on the league website revealed the instruction, which followed a complaint from the NFL Referees Association after Baltimore Ravens coach John Harbaugh yelled at a referee with his mask down earlier this month.
The NFL requires coaches wear masks at all times.
"All individuals must keep their masks in place when interacting with game officials on the field," the memo said.
"We have seen multiple occasions where head coaches have removed their masks to communicate with game officials during games. Doing so creates unnecessary, increased risk for the game official, the head coach, and others."
Other potential punishments against coaches violating the mask rule include fines, suspensions and the forfeiture of NFL Draft selections.