The three teams being fined are the Seattle Seahawks, Denver Broncos and San Francisco 49ers.

The three head coaches of the teams, the Seahawks' Pete Carroll, the Broncos' Vic Fangio and the 49ers' Kyle Shanahan were also each fined $100,000.

The NFL's executive vice president of football operations, Troy Vincent, sent a memo to all 32 of the league's teams a week ago calling on coaching employees to wear their masks at all times, CNN reported. Vincent warned in the memo that failure to follow the public health guidelines would result in sanctions.