The operation comes after former Socialist prime minister Jose Luis Rodriguez Zapatero was placed under formal investigation last week, in one of many corruption cases piling pressure on Prime Minister Pedro Sanchez’s government.

Agents from the UCO, a specialised unit of Spain’s Guardia Civil handling complex and sensitive investigations, went to the party’s headquarters on Wednesday to demand the documents, according to a judicial source, confirming a report by the El Confidencial newspaper.

“The operation is linked to an inquiry into alleged irregularities within the SEPI state holding company involving former party member Leire Diez,” the newspaper added.

The head of the main opposition conservative People’s Party (PP), Alberto Nunez Feijoo, said Sanchez’s government “stinks” of corruption and renewed his call for early elections.

Sanchez was at the Vatican on Wednesday ahead of a visit by Pope Leo XIV to Spain next month and was due to hold a press conference later in the day, his first since Zapatero was placed under investigation.

The Zapatero affair is one of several cases of alleged corruption involving members of the prime minister’s inner circle.

His brother, David Sanchez, is scheduled to stand trial for influence peddling, while his wife, Begona Gomez, is under investigation in a separate corruption case.

Sanchez has dismissed the cases against his family members as baseless and part of a right-wing “smear campaign”.

Sanchez’s former right-hand man, ex-transport minister Jose Luis Abalos, is also awaiting a verdict in his own corruption trial, which heard closing arguments earlier in May.

Zapatero, a Sanchez ally who governed Spain from 2004 to 2011, is under investigation for alleged irregularities linked to the state-backed rescue of an airline.

Zapatero has denied wrongdoing.