The sting operation, carried out in cities across Spain including Tarragona, Castellón, Alicante, Málaga, Cádiz and Ceuta at the request of Spanish anti-corruption prosecutors, targeted suspected members of the Polverino clan, added the source, speaking on condition of anonymity.
The arrests of clan members were for crimes including money laundering, forging official documents, Spanish news site El Confidencial reported on Tuesday.
Polverino members are also suspected of shipping hashish from Morocco to Spain and then to Naples in southern Italy.
According to Italian police, the clan's leader, Giuseppe Polverino, controlled part of the traffic in drugs between Spain and Italy and an empire worth around a billion euros ($1.3 billion).
He was arrested in March 2012 in Jerez de la Frontera in southern Spain.
Members of the Polverino clan are wanted in Italy for membership of a mafia association, attempted murder, extortion, usury, illegal possession of weapons, drug trafficking and money laundering.
The group, which operates in the northern suburbs of Naples, is also accused of importing hashish into Italy from Spain.
Spain's proximity to Morocco, a major hashish producer, and its close ties with its former colonies in Latin America, a major cocaine-producing region, have made it a key entry point for drugs bound for Europe.
The Polverino drugs are moved inside trucks that enter Spain via the ports of Valencia and Barcelona, according to Spain's El Confidencial newspaper.
Several Italian mafia clans have transferred their more risky activities such as drug trafficking to Spain, according to Italian journalist Roberto Saviano, the author of "Gomorrah," the best-selling expose on the criminal underworld in Naples.
Camorra bosses refer to Spain's Mediterranean coast as "Costa Nostra", or "our coast", alluding to the Sicilian mafia "Cosa Nostra", according to Saviano.