increase in promotion

We have a checker who is for promotion as a machine operator, they undergo a departmental assignment for 6 months wherein indicated in their papers that there will be a corresponding adjustment after passing the DA. However, if we give the checker an increase there would be problems to other machine operators who have been in the position longer than her, because she is currently receiving the same salary. MY question is, will we have problems if we do not give her an increase despite the fact that she was informed that she would have an increase if she passes the departmental assignment? Or can we use the fact that it is Managment prerogative? Thanks in advance.

if you have already informed her that she will get an increase.. then you should honor your word.. don't worry about the other Machine Operators.. as salary should be confidential..