How can we become permanent employee ??

Dear sir, i have been working with the reputed national institute of technology (NIT) of india for the last 15 years. first 4 years of job as daily wager, then 5 years on fixed pay and then and now again they put us on daily wager. now the institute (college) management is forcing us to join under service provider... they are paying us sate government rate from the last many years which is very low in compare to central government rate as we are working with the central government but they are paying us state government rates and they pay central government rate and also cut the PF to the workers who are working in the service provider. they are also not cutting PF from our salary..NO PF, NO Medical facility, NO Leave. Our institute follows 5 days a week but they are forcing us to come on Saturday also and if u not then they cut money from the salary.. now they are mentally torture us to join under Service Provider or leave the job . sir, need your urgent advice in this matter. sir, there are around 200 workers working in the institute who are facing the same problems How can we save ourslef from this situation.