Promotion regulation and recruitment

I am working in Punjab State Transmission Corporation Limited (PSTCL, State Govt. Undertaking) as a Junior Engineer/ Information Technology (JE/IT) since 2017. The post of JE/IT was created and filled for the 1st time in 2017 under separately created New IT cadre. There are other cadres in our organization like electrical, civil, accounts etc. but ours is separate and not linked to others. In our organization apart from JE there are posts of Assistant Manager/IT (AM/IT, equivalent to AE or SDO) under IT cadre. AM/IT are above JE/IT in organization hierarchy. Till recently the service regulation for the post of AM/IT was that all the posts of AM/IT are to be filled through recruitment (100% through direct recruitment). At the time of our recruitment the promotion channel of JE/IT was not defined i.e. at what post we will get promoted after JE/IT and after how many years. We requested our management to get our promotion channel created & it was created in September 2021. Under new regulation 50% of the posts of AM/IT are to be filled through promotion from JE/IT after completing 8 years as JE/IT & remaining through direct recruitment. Earlier in July 2021 i.e. before creating regulation, the process to recruit 01 AM/IT was started citing 100% direct recruitment regulation of AM/IT, which exist earlier. Due of this recruitment more than 50% posts of AM/IT will be filled through direct recruitment, leaving only 01 post for promotion. As new AM/IT is expected to join in November 2021, we requested our management to cancel the recruitment as it will jeopardize our career progression. However, management has replied that the recruitment can’t be cancelled as the recruitment process was started before new regulation on JE/IT promotion came into force. Moreover, they are saying that the recruitment of AM/IT is completely valid because when recruitment started regulation for AM/IT posts was 100% through direct recruitment. Now my questions are 1. Whether the points mentioned by our management to not cancel the recruitment, valid? 2. If not valid please specify how should proceed to stay the recruitment (please specify the ground on which I should fight and any other input related to this matter)?