FIFA has opened disciplinary proceedings against Mexico after alleged anti-gay chants by fans during their World Cup win over Germany on Sunday.

Some Mexican supporters chanted a slur when Germany goalkeeper Manuel Neuer prepared to take a goal kick in the 24th minute, and Mexico’s football federation (FMF) confirmed that FIFA had informed it of an official investigation.

Mexico fans have long shouted an insult at goalkeepers that rights groups argue is discriminatory. Those who have defended the chant insist there is no intent to discriminate.

During World Cup qualifiers, FIFA fined Mexico and a number of other Latin American teams several times over the slurs. The Court of Arbitration for Sport cancelled two fines against Mexico in November, although it also ruled the chant was “insulting” and left other fines in force.

Mexico’s federation has in the past appealed to fans to refrain from using the chant, and the effort was largely successful at last year’s Confederations Cup in Russia.

For the past month, the FMF has run an educational campaign asking fans to avoid using the chant. The federation tweeted a warning hours before FIFA’s announcement that those who chant the slur could find themselves barred from stadiums.

“In Russia, avoid being detained having your fan Fan ID taken away. Remember that you represent the best fan base in the world,” read the tweet — which also included a photo that wrote out the slur in question.