A Spanish court on Tuesday summoned Mariano Rajoy to testify as a witness in a major graft trial, the first time in modern history that any Spanish prime minister has had to take the stand.
The so-called Gurtel trial centres on a vast bribery network allegedly involving former members of Rajoy's Popular Party (PP), weakened by repeated accusations of graft.
While Spain's 62-year-old leader is not accused of anything, his post as party chief since 2004 means he could provide valuable testimony.
"They have called him as witness," a spokesman for the National Court that deals with major corruption cases said, adding that no date had been set yet for the hearing.
Jaume Munoz Jofre, a historian and author of Corrupt Spain: a brief history of corruption said the move is unprecedented.
"Rajoy will be the first acting prime minister who has to appear in court as a witness - Jaume Munoz Jofre
The only comparable events since Spain's transition to democracy following dictator Francisco Franco's 1975 death, he added, were the court appearances of two former prime ministers.
Felipe Gonzalez, an ex-Socialist leader, and Adolfo Suarez, prime minister during the transition, both testified as witnesses in separate trials in 1998.
A source at Rajoy's office, who refused to be named, said the government was "always willing to collaborate with judicial authorities as is normal in a democracy."
The Gurtel case allegedly saw companies shower former PP lawmakers and civil servants with bribes in exchange for contracts.
Altogether, 37 defendants face justice including two former party treasurers and businessman Francisco Correa, the alleged head of the network.
Spain is that country where the prime minister has to testify in corruption trial and only surprise is that he can’t order it not to happen
— South Of Watford (@Graeme_SoW) April 18, 2017
The PP denies any senior party officials were involved in any cases of alleged corruption. It says only a tiny number of its politicians are corrupt and that it is tackling the problem.
The complex, multi-stranded trial has already seen prison sentences handed down to three businessmen in February for their roles in a kickback scheme. The trial is ongoing.
Corruption is a major issue in Spain — which last year scored its worst ranking in Transparency International's annual corruption perceptions index — with the PP, rival Socialists and regional politicians hit by scandals.
In February the husband of Spain's Princess Cristina was sentenced to over six years in prison on charges including fraud and tax evasion.
Such is public anger over the issue that many voters have flocked to two relatively new parties — the far-left Podemos and the centre-right Ciudadanos.
As a result, although the PP still won a general election last year, it failed to retain the absolute majority it won in 2011, and Rajoy now heads a minority government.