ZURICH (Reuters) - Players will no longer be able to raise their shirts and reveal a slogan or message on an undergarment even if it is one of solidarity following a decision by soccer's rule-making body on Saturday.
The International Football Association Board (IFAB) also sanctioned the official use of headwear for women, after a two-year trial period, as well as for men.
Overt slogans have long been banned by FIFA, world soccer's governing authority, but players often lift up their shirts after scoring to show other messages like birthday greetings or a message for the birth of a baby.
"From now on there can be no slogan or image whatsoever on undergarments even good-natured ones. This will apply from June 1 and will be in force for the World Cup," FIFA secretary general Jerome Valcke told a news conference after an IFAB meeting.
Although many slogans that players display are of solidarity, Valcke said it had been decided to impose a blanket ban to avoid confusion.
"It's easier to say no," he said. "Sometimes, we are criticised for saying no but what is the definition of a nice message?"
Board member Jonathan Ford, chief executive of the Football Association of Wales, said it would be too complicated for match officials to determine what is a political or commercial message rather than one of solidarity.
"Some of this did think this might appear churlish but to determine what is right and wrong between different countries and cultures is very complicated, so it's easier to say it's got no place in the game." he said.
Players who break the rule will be punished by competition organisers rather than receiving a yellow card.
On head gear, FIFA ratified the use of head scarves for women, a measure which had been provisionally approved in July 2012 mainly so that women Muslim players could use the hijab.
"We had a request from the Sikh community to play with headgear and to avoid discrimination against men, it was decided that what applied to women can apply to men," added Valcke.
"We will work exactly on the definition on these covers."
IFAB, comprising the four British associations and four representatives of FIFA was formed in 1886 and predates the founding of FIFA by some 18 years.
The body, which is undergoing changes of its own with the introduction of technical and football sub-committees, sanctions and changes the laws after at least a three-quarters majority in favour of any proposal.
Valcke added the laws themselves are undergoing a revision to make their meaning, and their interpretation, clearer internationally.
(additional reporting by Mike Collett; editing by Tony Jimenez)