OVIEDO, Spain

After refusing to testify in a corruption probe against his wife on Tuesday, Spanish Prime Minister Pedro Sanchez filed a lawsuit against the judge leading the investigation.

The lawsuit was reported just hours after the judge, Juan Carlos Peinado, traveled to the Spanish government offices to interrogate Sanchez -- an unprecedented scene in Spain's modern political history.

Sanchez, who was questioned not as the prime minister but in a private capacity, used his right not to testify against his wife.

According to lawsuit documents seen by Spanish daily El Pais and other news outlets, Sanchez's lawyers allege the judge departed from traditional methods and failed to justify his highly publicized visit to the Moncloa Palace.

Peinado is accused of prevarication, which, under Spanish law, refers to a judge or civil servant who issues an arbitrary decision with the knowledge that it is unfair.

Sanchez's wife Begona Gomez is being investigated in a wide-ranging corruption probe about whether she used her influence as the prime minister's wife to influence contracts or set up a master's program.

In April when the judge accepted the case, brought about by far-right pressure groups, Sanchez threatened to step down as premier, denouncing it as “bullying” and “political harassment.”

On Tuesday morning, a lawyer for the far-right Vox party joined the judge to question Sanchez as the representative of the accusation.

According to Spanish law, the prime minister should have the right to reply to any of this type of questioning in written form.

Spain's public prosecutors agreed, but the judge refused to accept written testimony, saying he was questioning Sanchez as a private citizen, not as a government official.

The unconventional method of collecting Sanchez's statement ultimately brought about the lawsuit against the judge.

According to the lawsuit, since Sanchez's wife is being investigated for her connection to the prime minister, it does not make sense that his role as prime minister would be considered irrelevant.

“Therefore, it is legally incomprehensible that (the possibility of Sanchez testifying in writing) is dismissed," read the complaint, as reported by El Pais.

“There is a long history of how judicial resolutions can influence the political future of a country… it is evident, therefore, that the form of statement-taking makes a difference,” it added.

As the judge visited Madrid's government offices, protesters gathered nearby calling Sanchez and his family guilty and corrupt.

The probe against Gomez has been controversial.

When she was first summoned to testify, her declarations were suspended because her lawyer argued that she was not informed about the accusations against her.

When Gomez returned to the court earlier this month, she also refused to testify. Her lawyer later told the media that she did not cooperate because the judge said all of Gomez's activities since her husband became prime minister would be investigated.

“Our position is that the process lacks any clear goals … a judge cannot investigate anything, there should be limits to guarantee the rights of those under investigation,” her lawyer said at the time.

Meanwhile, Spain's main opposition party says their refusal to testify makes them all the more suspicious.

“It looks bad,” Popular Party spokesperson Miguel Tellado told media on Tuesday. “Spain doesn't deserve a government that lies and steals.”