ZURICH — Players at the World Cup face FIFA disciplinary action for revealing any slogan or image on their undershirts.
Soccer's rules-making panel modified the law on Saturday and it will take effect on June 1.
The panel, known as IFAB, says breaking the rule is not a yellow-card offense, though players can be disciplined by competition organizers.
Also, IFAB approved head coverings for male and female players and restated opposition to video replay in decision-making.
The panel rejected UEFA's proposal to remove red cards from the so-called "triple punishment" for penalty-area fouls, which deny a goal-scoring opportunity.
IFAB's new soccer and technical advisory panels will discuss the issue and oversee trials of "sin bins" where players are sidelined for several minutes instead of getting a yellow card.