Spain's National Court has opened a probe into allegations of slush fund payments by the ruling Popular Party's former treasurer to leading members, including Prime Minister Mariano Rajoy.
The court said on Thursday that Judge Pablo Ruz had asked prosecutors for documents published recently by leading newspaper El Pais that allegedly showed lists made by former treasurer Luis Barcenas of payments to members and donations from companies over about 20 years.
Mr Ruz last week withdrew Mr Barcenas' passport as part of a related probe into how he once amassed 38 million euro (£33 million) in Swiss bank accounts.
The Barcenas scandals have rocked Mr Rajoy's party although the party denies all wrongdoing.
A government poll released on Wednesday suggested Spaniards now rank corruption as the country's second biggest problem after unemployment.