The stolen chairs, which had an estimated value of €60,000, were resold in Spain, Morocco and Romania, according to police.
Spanish police have arrested seven people suspected of stealing more than 1,110 chairs from restaurants and bars in Madrid and another nearby municipality in just two months.
The criminal gang of six men and a woman worked at night to steal chairs that had been stacked in outdoor seating areas while the establishments were closed, according to Spain's National Police.
At least 18 different establishments were targeted in Madrid and Talavera de la Reina, a smaller city to the southwest of the capital, in August and September.
The estimated cost of the stolen chairs was around €60,000, authorities said.
The suspects, who face charges of theft and belonging to a criminal organisation, resold the chairs not only in Spain but also in Morocco and Romania, according to police.
The investigation began when police received several complaints from restaurant owners left with fewer chairs than they had left stacked the night before, local media reported.
In Spain, many restaurants and bars leave tables and chairs, which are usually made of metal or hard plastic, outdoors during the night.
The chairs are normally kept in stacks and chained down.