Seniority Issue in matter of departmental candidate and direct recruited candidate

Commercial taxes department, Rajasthan have Tax Assistant Post which filled by 2 Ways:- 1. Limited direct recruitment examination for departmental candidate already in service in commercial taxes department as LDC or UDC. (20%) 2. Direct recruitment examination (80%) In first ever recruitment year (2011) government prefer departmental candidate and conduct examination for 1st category than conduct examination for 2nd category but in next recruitment year (2014) government didn't conduct examination for departmental candidates and firstly recruited direct candidate after that conduct exam for departmental candidates. Hence departmental candidates remain junior from direct candidate. At the time of recruitment procedure started (2014) departmental candidates was eligible for selection but due to non conduction of exam they remain junior. Departmental candidates are in department from so long and they should have right for first choice for new post. So please give advice how to go forward in legal/litigation directions to challange wrong behaviour of department/government.