Advice needed – reduction in job hours

Treacle_2-2

My mum has is just in the process of finding out her job is changing – she’ll be able to do her work in two hours a day instead of four. Does anyone know how she stands with regard to if it’ll affect her pension? Also how the law stands as to her rights. She’s been with the company for 20 odd years and is just waiting for early retirement or redundancy. Can the company make her work less hours or make her take on some extra work ? Just unsure if she’ll be given a choice or if she will be told what she has to do!