"Several people have been detained... and searches are under way in livestock farms, private estates, veterinary clinics and slaughterhouses" around Spain, a Civil Guard spokesman told news agency AFP.
Police are investigating the suspected "introduction of horses into various slaughterhouses in Spain with forged or altered identification and health documents, to make meat for human consumption" in breach of norms.
The spokesman, who asked not to be named, said French police were also taking part in the raids.
Several suspects were detained in France in December during similar investigations.
The Civil Guard source could not say exactly how many people were arrested in Spain.
A health scare erupted across Europe last year after probes revealed horsemeat was mislabelled and sold as ready meals containing beef.
A Dutch businessman at the heart of that scandal was charged with fraud in France last month.