Issuing of NOC from psu for state public service commission.

Sir currently i am working in a public sector undertaking. I have completed 7 years in this organization. Recently my employer has made a new circular regarding issuance of NOC, that " employee will not be issued any type of noc or employee cannot apply for any outside organization within the two years of promotion". Also they made a rule for seeking approval when applying for outside employment if the employee is not in the two years period of promotion. My question is can I challenge these two rules? Secondly i want to apply for state public service commission. This type of exam takes almost three years to complete the procedure (preliminary, mains, interview). So if I apply before my promotion for preliminary examination with proper intimation and approval and after that within three years I get promotion(which is scheduled next year) then can my employer deny me or refrain me from sitting main examination (of that year for which preliminary exam i was eligible as I had not any promotion during prelims) as the form fill up procedure of the same require intimation to employer in each stages of examination.