Barcli,
In this case though it is a holding company that owns company A and is now buying company B. While they are kept separate the holding company can do whatever it wants to the newly bought company.
This was the case recently when Kraft bought Cadbury's and closed a factory it promised to keep open and transfered production to other factories with spare capacity and cheaper production. see here:
Kraft to close Cadbury plant it offered to keep open - Telegraph Those working at the closing factory had no right to the jobs at other Cadbury's factories of employees who had been at the company for a shorter period of time, let alone at other Kraft factories in general.