The alleged offences include belonging to a criminal organisation, bribery, disclosure of secrets, inducement to give false testimony, false accusation, falsification of commercial documents, misconduct in public office, influence peddling and offences against state institutions.
At a news conference in Rome after meeting Pope Leo, Spanish Prime Minister Pedro Sanchez stressed Wednesday's request for documents did not constitute a police search, adding the party was fully co-operating with the courts and had absolute respect for the judiciary.
Investigating judge Santiago Pedraz ordered the request of various documents and electronic files from the party's headquarters, the court said.
A judicial request for information requires prior notice and targets specific items, as distinct from an "entry and search" carried out without prior notice to gather all kinds of evidence.
Pedraz's investigation centres on former organisation secretary Santos Cerdan, along with other party officials, lawyers, a businessman and a police officer.
It is the first time Cerdan has been named in this case. He has denied wrongdoing in another investigation.
The party led by Sanchez has been dogged by a slew of corruption scandals, including various investigations into Sanchez's key allies and family members.
Sanchez said if new irregular behaviour emerged, his party would deal with it with the same firmness as before.
Last week, the High Court said it was investigating Jose Luis Rodriguez Zapatero - a former Socialist premier and close Sanchez ally - on suspicion of leading an influence-peddling and money-laundering network, dealing another blow to the leftist coalition government.
Zapatero denied any wrongdoing, and Sanchez on Wednesday reiterated his support for his predecessor.
