Discrimination in appointment in ONGC ltd.

Dear Sir, I am working in ONGC as l Assistant Technician (A2 Level) since 2012 Asking Qualification for the post is 3 years diploma in engineering .Pay Scale is [deleted]. Promotion for Class-III employees in ONGC is after every 6 years irrespective of qualification. Let me elaborate- A2 level [deleted] A3 level [deleted] A4 level [deleted] E0 level (Officer Cateory) [deleted] It takes 18 years to reach E0 level from A2 level. But my point- There is a Memorandum of Understanding between Management of ONGC and Recognized Unions, signed in 19 August 2004 approved by the Executive Committee of ONGC. but before MoU2004 there is a MRPR1980 for regulating thr Recruitment and Promotion . according to MRPR1980 the induction of diploma engineers was A4 . my question is that sir, is it legal to recruit manpower by adopting a MoU instead of a full-phased R&P policy. We are very demoralised sir. It is a huge degradation. So please guide me what can we do. Can we go for legal assistance? will it be fruitful?