Prosecutors allege that Grupo Villar Mir (GVM), the private holding that the 85-year-old industrialist has spent the past 30 years building up, won the contract in 2006 by rigging the auction. Villar Mir has always denied any wrongdoing.

GVM owns a majority stake in Spanish builder OHL (>> Obrascon Huarte Lain SA). After the allegations first surfaced in 2006, the contract worth 600 million euros (510.76 million pounds) was handed to a subsidiary of another Madrid-listed builder, ACS (>> ACS Actividades de Constrccn y Srvcos SA).

Reuters could not immediately reach Villar Mir, an influential business leader who sits on the board of Spain's biggest bank Santander (>> Banco Santander, S.A.).

He will be questioned on Jan. 9 via video link along with six other people involved in the tender to build the Son Espases hospital on the island of Mallorca, Judge Jose Castro wrote in a court ruling.

Villar Mir and his family have the fifth-biggest fortune in Spain, valued at $3.1 billion according to Forbes. Villar Mir passed on the chairmanship of OHL to his son in July.

(Reporting by Rodrigo Miguel; Writing by Angus Berwick; Editing by Richard Lough)