They face charges of animal abuse, documentary falsification, prevarication, crimes against public health, money laundering and belonging to a criminal organisation.
A Dutch national has been arrested in Belgium and authorities suspect that he is the mastermind behind the operation. Europol reported Sunday that a Dutch citizen is believed to be the head of the horsemeat trading gang and was arrested in Belgium on various charges including crimes against public health and forgery.
The investigation is related to 2013's horsemeat scandal, which came to light after the Food Safety Authority of Ireland found that 10 out of 27 hamburger products it analyzed in a study contained horse DNA.
Ten million burgers ended up being taken off shelves and sales fell by 43 per cent.
The meat was sold across Europe and may have earned the group over 20 million euros ($23 million) per year, Spanish police said in a separate statement.
A French supplier, Comigel, which supplies products to customers in 16 countries, was at the time implicated in the scandal.
The group of criminals got the horses from Spain and Portugal.
This led to Guardia Civil initiating Operation Gazel which examined unusual behaviour in horsemeat markets in Europe including the forging of animal identification.
He was in 2016 identified as the ringleader of a racket in which horses "in bad shape, too old or simply labelled as "not suitable for consumption" were killed in two abattoirs in northern Spain, and sent to Belgium after their certifying documents were altered.
The Europe-wide investigation eventually led the Guardia Civil to the Dutch businessman, who is said to be "known in the horsemeat world".
"This person managed this network from the shadows, using men of confidence in each of the territories in which it was present", the Civil Guard rep revealed.
Several bank accounts and properties were blocked or seized, and five luxury cars seized, Europol said.
The group is suspected of having modified the horse's microchips and documentation to pass off the meat as edible.