It is something that both parties hate to do, it is something unavoidable though, it will happen at some point in anyone's career. It is always initiated by the employee (if you know something different this will be a global exception), it is not a pleasant situation since there must be a reason for requesting negotiation for the one party and for the other party there must be a very well proposition / opposition:
- either to satisfy partially or fully the request(s) or
- not to demotivate you if there will be a "diplomatic rejection" of the request for the specific period.
Negotiation does not always have losers or winners, the best is to have a balanced situation. Usually this can happen when there is good timing for both parties, good argumentsm, faith and persuasive skills.