If an employee is told that they are going to transfer to a new employer, they have a number of options.
1. They can resign
2. They can accept the transfer and become an employee of the new employer
3. They can object to the transfer
1 and 3 are not the same. An objection to the transfer is not a resignation. This is important if the employee wishes to bring an unfair (constructive) dismissal claim because an employee can not make such a claim unless they have resigned (in circumstances where they resign in response to a fundamental breach of contract by the employer). Objecting to the transfer will not allow employees to treat themselves as constructively dismissed.
Employees who object to a transfer fall through the gap between a dismissal and a resignation, unless the employee would (not might) suffer a substantial change in working conditions to their material detriment after the transfer, in which case the objection to the transfer can amount to a dismissal.