Encroachment of Common Areas by Society Members

Hello, I am a member of a Co-Op Hsg. Society ( Commercial Building ), some of the members of the Society ( Managing Committee Member ) have illegaly occupied common passage areas of the Society. I have written various complaint letters to the society pointing out the irregularities and requesting them to take action against the erring members. Unfortunately the chairman and the secretary are one amongst the biggest encroachers of the common area of the society, hence the society is not taking any action. Their Defense is that the Builder had sold them to the members in that condition and the same is in as wherein basis from the day the society was handed over by the builder to the Society. I have several times pointed out that as per the Local Muncipality Approved Plan the same is Common Area and even if the Builder has sold to them, it is illegal and needs correction from the Managing Committee,but it falls on deaf ears as they are biggest beneficiary of the same. I have written to the Local Municipality but they have failed to take action as they erring members have managed them and they are compromised. My question is what action can i take, Can I make the Society a party to the case, since the society is not ready to take action. How much time will it take and what will be the costs involved.