Spain's High Court on Thursday placed Antonio Brufau, chairman of oil company Repsol, and Isidro Faine, the former chairman of Spain's Caixabank, under formal investigation as part of a probe into a decade-old alleged spying case.

An official court document released on Thursday showed the judge is investigating whether Repsol and Caixabank hired Grupo Cenyt, a security firm belonging to former police chief Jose Manuel Villarejo, to spy on the then chairman of construction company Sacyr, Luis del Rivero, in 2011 and 2012.

The alleged aim was to block a takeover bid for Repsol by Sacyr and Mexican state oil firm Pemex.

Repsol was then partly owned by Caixabank.

The so-called 'WINE' project allegedly started when Repsol detected a common "strategy by Del Rivero to join (forces) with Pemex in order to obtain almost a third of the total shares of Repsol, and thus gain control of the Spanish oil company," the court document said.

Repsol said no current or former board member, executive or employee had acted illegally or unethically in relation to the procurement of information services. urn:newsml:reuters.com:*:nL1N2M815A

Caixabank declined to comment. Reuters was not immediately able to contact Pemex representatives or lawyers of Brufau and Faine.

A source close to Faine said he would only make statements in court and had not yet decided on his defence.

The decision by investigation judge Manuel Garcia Castellon means Brufau and Faine will be investigated for any possible links to bribery, in connection with both companies' alleged dealings with Villarejo.

Under the Spanish judicial system no formal charges can be brought until the first phase of investigation is over and being under investigation does not necessarily mean there will be a formal indictment.

The investigation is part of a wider inquiry, with Villarejo at the centre, that has roiled Spain's corporate sector, causing some reputational damage, but with no clear impact on businesses so far. 

(Reporting by Jesus Aguado; additional reporting Isla Binnie; Editing by Emma Pinedo, Inti Landauro and Susan Fenton) ((jesus.aguado@thomsonreuters.com; +34 91 585 8339; Reuters Messaging: Reuters Messaging: jesus.aguado.reuters.com@reuters.net))