The former Spanghero workers were taken into custody in connection with the judicial inquiry opened in Paris in March.
Spanghero (now La Lauragaise) has been pinpointed by the government as a key player in the European scandal.
French authorities have said Spanghero knowingly sold 750 tonnes of horse meat mislabelled as beef over six months.
The firm closed in June and resumed activities two months later with the changed name and new management.
The news follows the arrest of two men in the UK earlier this year on suspicion of conspiracy to defraud and two other men being interviewed under caution.