Dispute in contract

I am having  a case of government contractor, who is doing a government contract. he has completed the 90% work of the contract. His payment is due from last two years, nor the payment is getting released nor his work is gettiing terminated. he has got notice to terminate the work long back but no one is taking over the site. since he has not got the payments, he is not able to leave the site and his cost is esclating on daily  basis. how should he proceed. please guide.