Police in Patra have arrested eight people and are seeking another four in connection to alleged bogus marriages that were used to help migrants obtain residence permits.
One Greek man, four Greek women, two Nigerian men and one Nigerian woman were arrested in the port city.
Another Greek man and men from Nigeria, Afghanistan and Senegal are being sought.
The gang allegedly paid Greek women up to 500 euros to marry irregular migrants or to claim that they were the fathers of their children.
The suspects face charges of forming a criminal gang, fraud and making false declarations.