MADRID- Spain's High Court on Monday placed Antonio Brufau, chairman of oil company Repsol, and Isidro Faine, former chairman of Spain's Caixabank, under formal investigation for a second time as part of a decade-old alleged spying case.

Last year, investigating judge Manuel Garcia Castellon dismissed a probe into Brufau, Faine, Repsol and Caixabank, but three different judges decided on Monday to accept appeals from the prosecutor, the former chairman of construction company Sacyr SCYR.MC and left-wing political party Podemos.

Caixabank declined to comment. The Caixabank Foundation, which Faine chairs, declined to comment on his behalf. Repsol did not immediately reply to a request for comment.

Faine and Brufau and the companies have previously denied wrongdoing.

The High Court is investigating if Repsol and Caixabank hired a security firm belonging to former police chief Jose Manuel Villarejo to spy on Luis del Rivero in 2011 and 2012, when he was chairman of Sacyr.

The court is trying to establish whether Repsol and the bank, which at the time held a stake in the oil company, hired Villarejo to help fend off a takeover bid for Repsol from Sacyr and Mexican state oil firm Pemex.

Both Repsol and Caixabank have previously pledged to fully cooperate with judicial authorities.

Under the Spanish judicial system no formal charges can be brought until the first phase of investigation is over and being placed under investigation does not necessarily lead to 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 Emma Pinedo Additional reporting by Jes?s Aguado and Isla Binnie Editing by Mark Potter) ((emma.pinedo@thomsonreuters.com; +918 35 68 34;))