To be honest, I'm surprised it's took them this long to do it.
No doubt when Go-Ahead acquired the depot, the employees will have been transferred over and been allowed to keep their original contract terms, and they want to move them over to an equivalent contract to that of the other subsidiaries.
The exact same thing has happened with most of the supermarkets over the last few years, where the older employees were on very old contracts which were very generous with the benefits they offered.
RE: North West Bus Operations