Rights groups have called on footballing body FIFA to apologise for failing to tackle the use of gay slurs at the World Cup.

This year’s World Cup has been noted for the use of the repeated anti-gay slur ‘puto’ (faggot/male prostitute) by Mexico and Brazil crowds, but FIFA declined to take action, claiming the slurs were “not offensive”.

An open letter to FIFA President Sepp Blatter, signed by representatives from 25 groups, including GLAAD, Outsports and the Human Rights Campaign, threatens to get at the World Cup through its sponsors, if the issue is ignored.

It reads in part: “The lesbian, gay, bisexual, and transgender (LGBT) community and its allies were extremely disappointed and surprised by FIFA’s recent decision to affirm use of the anti-gay slur ‘puto.’

“Conapred, Mexico’s anti-discrimination agency, has come out strongly stating that the word is offensive and hurtful, so it is perplexing that FIFA has determined otherwise.

“Sadly, the negative effect of your decision quickly manifested. During the 23 June telecast of the World Cup, fans of team Mexico chanted ‘puto’ more times than ever, along with other anti-gay slurs like ‘culero.’

“FIFA seems only to have popularized words that, in many parts of the Spanish-speaking world, mean ‘faggot’.

“FIFA’s own statutes specify that it would expel fans for discriminatory behavior, yet you are taking no action whatsoever.

“By not addressing the use of anti-gay slurs in advance of the World Cup and by not speaking out against their use now, FIFA is endangering the wellbeing of LGBT sports fans both in its venues, as well as those watching at home.

“Some World Cup sponsors and advertisers have been forced to compromise their own values, which demand respect for LGBT people and customers.

“If FIFA continues to turn its head the other way and tacitly condone anti-gay discrimination, we will be left with no choice but to express our very grave concern to your sponsors, several of which have a long history of speaking out against anti-LGBT bias.”