Last week, England midfielder Jude Bellingham was not sent off despite covering his mouth while speaking to Ghana’s Jordan Ayew.
Before the tournament, Fifa’s head of referees Pierluigi Collina explained players were permitted to hide their mouth if engaging in “friendly conversations”.
He said the new law was designed for “confrontational” interactions.
The decision to implement this new rule was taken during a special meeting of the law-making International Football Association Board (Ifab) in Vancouver in April.
Fifa president Gianni Infantino had previously spoken in support of such a punishment being rolled out, saying referees should work from a “presumption” that players have said “something they shouldn’t have”.
The issue of players covering their mouths came under the spotlight in February when Benfica winger Gianluca Prestianni raised his shirt while speaking to Real Madrid’s Vinicius Jr during a Champions League game.
The Argentina international was accused of racist abuse – which he denied – and provisionally banned for one match. Following a Uefa investigation, Prestianni was instead found guilty of homophobic conduct and banned for six matches – three of which were suspended.
Any decision to send a player off remains at the discretion of the referee, who will consider all circumstances before issuing a red card.