Pl see sec 10 of CL(R&A) Act 1970 and ensure that the contract labour are not engaged in the areas works which fall under this provision. It has to be decided based on the nature of activity in which you establishment is involved. Also each state and also central Government has specifically issued GOs prohibiting engagement fo contract labour in certain areas. If these are not taken care, the Government Authorities may direct you not to engage contract labour in these areas and amy prosecute for engaging CLs in prohibited areas.
If any contract labour is working continuously for 4 to 5 years and is engaged in the the activities which fall under sec 10 of the act, it is the state government to decide and pass order on the contravention of this provision.
However, there is no regulation or obligation on the part of the Principal Employer that the CL labour so engaged in the prohibited employment to be taken in the roles of the principal employer. There is no legal obligation on the part of principal employer to absorb any one who has completed 180 days of service or so.
Also you have to ensure that:
1. There is no sham contract. There must be a legal contractor who is having separate entity ie., a Registration under shop act, PF & ESI code etc., and it is always better we engage a contractor who works for more than one establishment so that he can manage to rotate the CL frequently from one co to another co.
2. Equal work to equal pay to be always kept in mind. For eg..a security guard in Principal Employer's rolls and a security guard in Contractor rolls performing same and similar duties at same wrokspor. etc.,