The Nature Protection Service of the Civil Guard (known as SEPRONA) revealed on Wednesday that "Operation Cato" began in January when 500 puppies a month were discovered being sold through means covered by the European Union's TRACES' Trade Control and Expert System.
This electronic database tracks the movement of animals and animal products both outside the EU and within its territory.
The 'pet passports' issued to the animals had been falsified, according to police sources.
A Civil Guard press release noted that SEPRONA followed the paper trail and discovered 180 of the puppies being transported in a truck near Fraga (Huesca) to a farm at an unspecified location.
They were due to be sold in Girona, Barcelona, Badajoz, Guadalajara, Malaga and Huesca.
A vet was arrested for having allegedly falsified the animals' documents.
The age of the puppies did not match the details on their paperwork and irregularities were found in their vaccination records.
The latest puppy rescue brings the total number of imported Slovakian pets intercepted by Spanish police to 595.
21,340 animals have been inspected in over 2,000 pet shops and other points of sale, leading to 1,309 prosecutions.