The paper is part of a group of 12 European news outlets that began publishing on December 2nd the results of months of investigations into a vast trove of more than 18 million financial documents, obtained by the German magazine Der Spiegel and dubbed the "Football Leaks".
The probe has centred on current and former players of the Spanish league such as Real Madrid star Cristiano Ronaldo, who won his fourth Ballon d'Or on Monday, and Manchester United coach Jose Mourinho, formerly of Real.
El Mundo said Spain's anti-fraud office Onif had ordered Unidad Editorial, the paper's parent company, to hand over "all information and documents with fiscal interest" related to the "Football Leaks" probe.
The newspaper said the anti-fraud office was seeking information on 37 people and bodies, including Ronaldo, his agent Jorge Mendes and his management company Gestifute.
Real Madrid's French striker Karim Benzema, FC Barcelona's Brazilian striker Neymar and Arsenal's German midfielder Mesut Ozil are also on the list.
Contacted by AFP, a tax office source confirmed the request for information had been made but did not confirm the names listed by El Mundo.
The newspaper's decision whether or not to turn over the documents that were requested will "depend on the authorisation of our sources", El Mundo director Pedro Garcia Cuartango wrote in a column.
The first leaks unveiled as part of the European Investigative Collaborations (EIC) journalists' consortium centred on "a system" allegedly put in place by Mendes, the agent of Ronaldo and Mourinho.
They allege for instance that Ronaldo could have "hidden €150 million (from image rights) in tax havens in Switzerland and the British Virgin Islands."
Both Ronaldo and Mourinho maintain they have fully complied with Spanish and British fiscal requirements.
Still, Spanish tax authorities are investigating the allegations where Ronaldo is concerned.
The EIC consortium which is carrying out the "Football Leaks" also includes Britain's Sunday Times and Portugal's Expresso.