Evaluating Contractor Payment and Compliance
Introspect—are you paying him too little? In your pursuit of getting the best rates, you may have hired a contractor who will compromise on ethics and mandatory obligations. Did you make your demands for statutory obligations clear before the project was awarded? Decent contractors, if informed beforehand of their obligations, will build that into costs. However, if your decision was made solely on "rates," you may have pushed your contractor into a corner.
If you have done everything right, just issue a show cause letter, demand an audit (if your contract allows it), and if found guilty, stop paying him pending a course correction window. If he continues to violate the contract, terminate the contract and move on.
If the fault is in your system, issue revised requirements, make it time-bound, renegotiate, include audit clauses, and proceed as above.