The judge Juan Carlos Peinado arrived on Tuesday at Pedro Sánchez's residence Moncloa to question him. Sánchez then said no, in accordance with a provision that one has the right to refuse to testify in cases involving close relatives.
The case is a corruption investigation against Begoña Gómez, following allegations that the Prime Minister has described as politically motivated. The suspicions have been presented by the anti-corruption group Manos Limpias ("Clean Hands") whose leader has ties to extreme right-wing groups.
Sánchez chose to respond by filing a lawsuit against Judge Peinado. The Prime Minister claims in the lawsuit that the judge may have committed "criminal acts" by not allowing written responses.
"This is not a frontal attack on the judiciary. On the contrary, it is an expression of confidence in the judiciary, which can put an end to these abuses", wrote the Prime Minister in his lawsuit.
In April, Sánchez threatened to resign, and called the process against his wife a threat to democracy.