Fifa's request comes after criticism from athletes and activists.
"In the context of the adoption of the federal law 'on prohibition of propaganda of non-traditional sexual relations' in Russia, Fifa has asked the Russian authorities for clarification and more details on this new law," the federation said.
Russia's President Vladimir Putin ratified the new law in June as part of a wider political crackdown but it has cast a shadow over preparations for the World Athletics Championships, currently being held in Moscow, and next year's Winter Olympics.
Calls have mounted for a boycott of the Games in the Black Sea resort of Sochi and even US President Barack Obama has weighed in, commenting that he opposed intimidation against gays, lesbians and transgendered people.
Fifa, whose request follows that of the International Olympic Committee last week, said its statutes and code of conduct "foresee zero tolerance against discrimination based, among other things, on sexual orientation".
It added: "Fifa expects that all guests in a Fifa World Cup host country whether they are fans, players, officials or media, experience a great Fifa World Cup irrespective of their sexual orientation.
"Fifa is firmly convinced that the staging of the Fifa World Cup can contribute to uniting people and having a positive social impact.
"Russia has committed to provide all visitors and fans with a warm welcome and ensure their safety. Fifa trusts that the 2018 Fifa World Cup hosts will deliver on this promise." – AFP