The Royal Moroccan Football Federation and striker Munir El Haddadi have appealed to the Court of Arbitration for Sport (CAS) in a bid to enable him to be included in their World Cup squad.
Spanish-born Munir, whose father was born in Morocco, played for Spain's senior side in a Euro 2016 qualifying match in 2014.
Last month, FIFA turned down an appeal by Morocco and Munir, who plays for Deportivo Alaves on loan from Barcelona, for him to be allowed to represent them.
"The Court of Arbitration for Sport has registered an appeal filed jointly by the football player Munir El Haddadi and the Moroccan Football Federation against FIFA and the Spanish Football Federation," a CAS statement said.
"Munir El Haddadi and the Moroccan Football Federation are challenging the decision issued on 13 March 2018 by the FIFA Players' Status Committee in which their request to have the sporting nationality of Munir El Haddadi changed from Spain to Morocco was rejected."
CAS said arbitration was in progress and both Munir and Morocco had requested a decision by mid-May "in order for the player's sporting nationality to be decided prior to the commencement of the World Cup."
FIFA rules forbid any player who has appeared in an official competition for one national team to represent another in an international match.
Morocco have qualified for the World Cup for the first time since 1998 and face Spain, Portugal and Iran in Group B.
Munir last featured for Spain in October 2016 when he played for the under-21 squad.
The 22-year-old has the support of former national coach Vicente Del Bosque, who recently said he "felt responsible" for the situation and regretted his decision to call Munir up to the senior side.