The Infanta Cristina, 47, Juan Carlos's youngest daughter, had appealed against the order for 10 years' worth of her income statements to be included in the evidence he is examining.
The demand stemmed from an investigation into allegations of embezzlement against her husband, the former Olympic handball player Inaki Urdangarin.
Cristina won some respite on May 7 when judges spared her for the time being from being called into court to be questioned as a formal suspect in the embezzlement case.
But they said she may yet be summoned to the court in Palma de Mallorca on the Balearic Islands in another branch of the affair: a tax and money-laundering case also linked to her husband.
The court said in a statement that investigating judge Jose Castro "dismisses the appeals lodged by the representatives of Inaki Urdangarin and Cristina Federica de Borbon y Grecia against the ruling that charges the tax authorities with providing their past 10 declarations of income".
It said the income statements "have not been incorporated into the case for the moment, pending the taking of certain decisions" that will determine the course of the tax fraud case.
Castro is investigating accusations that Urdangarin and his former business partner Diego Torres embezzled six million euros (eight million dollars) in public funds meant for sports events.
The money was allegedly placed in the non-profit Noos Institute, which Urdangarin chaired from 2004 to 2006 and of which Cristina was a board member.
Neither she nor Urdangarin has been charged with any crime.