Section 12(1)(iv) in The Assam Engineering (Irrigation Department) Service Rules, 1978
(iv)In case the Governor is satisfied that the Officer so taken to a department for a specialized work cannot be withdrawn from the work due to non-availability of any other officer of an equivalent status in the department for that work. The officer so taken to a department shall be granted all promotions proforma, whatsoever may be due to him in respect of his original service.