According to the report, Calatrava was paid $3.6 million for architectural models and design for a convention center in Castellon in 2008. The center was never built after Spain's economic crisis and resulting austerity drive.
The Valencia High Court has requested documents detailing how Calatrava was hired in private, without any publicity. For contracts over a certain minimum value, that is illegal in Spain.
Some public officials have also been charged in the case over the way the work was contracted. Calatrava is expected to appear before the Castellon provincial court on September 2.