The body governing Spain's judges on Monday urged Prime Minister Pedro Sanchez to respect court decisions after he criticised a summons for his wife to testify in a graft probe.

A Madrid court last week called Begona Gomez to testify on July 5 "as an investigated party", as part of a preliminary investigation over suspected influence peddling and corruption.

The investigation began in April following a complaint against her filed by an anti-graft NGO linked to the far right.

The summons came just six days before Spain voted in the EU elections, prompting Sanchez to denounce the timing as "strange" in a letter on X, saying the courts were normally careful not to issue such statements so close to a vote for fear of influencing the outcome.

He also said there was no basis for the probe, calling it a "crude set-up promoted by far-right associations".

Spain's General Council of the Judiciary (CGPJ) which is responsible for naming judges and ensuring the independence of both courts and judges, on Monday criticised Sanchez for making "a political assessment about the actions of an investigating judge".

"Judicial decisions may be subject to moderate and rational criticism by those who disagree with them" but they "deserve the utmost respect by all and, in a particularly qualified manner by those who are at the head of the institutions, without any exception whatsoever," it said in a statement.

"We once again call for restraint and to avoid any kind of judgement of intentions, which only contributes to the deterioration.. of constitutional democracy."

Manos Limpias (Clean Hands), which filed the lawsuit against Sanchez's wife, has admitted its complaint was based on media reports.

It has previously filed a litany of unsuccessful lawsuits against politicians.

The case concerns letters of support she allegedly provided for a joint venture bidding for several public contracts worth 10.2 million euros ($11.1 million).

Although it did not represent the cheapest bid, the joint venture received top marks in the sections on subjective appraisal, beating all its competitors in the final accounting.