Spanish investigators have searched several addresses in a crackdown linked to the long-running tax evasion scandal in Liechtenstein.
They targeted tax advice offices, investment companies and a private bank in an operation centred on Madrid, Barcelona, Malaga and Zaragoza.
The total amount of cash hidden from the Spanish taxman could be more than 200 million euros, according to authorities.
In the wake of a probe by German investigators into suspected tax evasion, Spain is one of a number of countries to have launched investigations.
The German enquiry put the spotlight on Liechtenstein, widely seen as one of the world’s most secretive tax havens. It saw the arrest of former Deutsche Post head Klaus Zumwinkel.
Berlin revealed that a former employee at Liechtenstein’s LGT Bank had sold customer data to German intelligence services.