Former Spanish Prime Minister Jose Luis Rodriguez Zapatero is under investigation over alleged influence peddling and related crimes in the  bailout of an airline during the COVID-19 pandemic.

The High Court said on Tuesday that Zapatero’s office in Madrid was searched along with three other premises. The socialist, who governed Spain from 2004 to 2011, was summoned to testify on June 2.

The investigation is tied to the 2021 state rescue of Plus Ultra, which received 53 million euros ($62m) through the state holding company SEPI during the pandemic.

The case escalated in late December after several arrests, including businessman Julio Martinez Martinez, known as Julito, who is considered key to understanding the links between Plus Ultra and Zapatero.

Zapatero is alleged to have been the driving force behind the airline’s bailout and is accused of having pressed the Ministry of Transport, then led by Jose Luis Abalos, to approve the rescue.

Suspicion also centres on Analisis Relevante, Julito’s company, which allegedly received the same amount Plus Ultra later paid to Zapatero. Víctor de Aldama, a Spanish businessman involved in other corruption probes, has alleged Zapatero received 10 million euros ($12m) in commissions.

In a video message, Zapatero denied having committed any wrongdoing.

“I want to reaffirm in the strongest possible terms that I have never carried out any dealings with any public administration or the public sector in relation to the bailout of Plus Ultra,” he said on Tuesday.

The bailout remained politically controversial because critics questioned both Plus Ultra’s financial viability and the company’s ownership links to Venezuelan businessmen seen as close to the government of then-President Nicolas Maduro, raising concerns about transparency and possible political influence.

The court is examining whether the aid was properly approved and whether any improper lobbying or influence was involved.

Speaking to the newspaper El Pais, the president of the Andalusian regional government, Juanma Moreno, said: “There has never been a serious investigation process, much less an indictment of a former president. This is something unprecedented and will shake up the government.”

The conservative opposition People’s Party has used the case to sharpen its attacks on Prime Minister Pedro Sanchez of the Socialist Workers’ Party, to which Zapatero also belongs. Sanchez’s administration is already facing separate corruption probes involving figures close to the prime minister as well as investigations touching his wife and brother.

Zapatero has long been a key ally of Sanchez and has also drawn criticism from the opposition over business and political ties with Venezuela after leaving office. He has denied wrongdoing before a parliamentary committee.