The Ministry has directed banks / to do away with their / separate promotion policies, a move / strongly opposed by the officers' unions.
A. The Ministry has directed banks
B. to do away with their
C. separate promotion policies, a move
D. strongly opposed by the officers' unions
E. No error
Answer: Option D

......"unions" is grammatically correct. It is possible that there can be a more than one union for the officers.
there may be more than one union of bank officers.
I second Mr.Devendra. "The" suggests there is only a single union, so the 's' should be omitted.
Officers' union