Melvin,
The transfer of an employee from one station to another is ordinarily considered as a prerogative of your employer. This is especially true in service oriented enterprise, such as banks, in order to satisfy its clients or to obtain reasonable return of its investment.
If you disobey the memo, that can be considered as Insubordination which is a ground for termination under our labor laws (Article 282).
But here's a kicker: Transfer of employees will amount to constructive dismissal when the same is unreasonable, inconvenient, or prejudicial, and it involves a demotion in rank or diminution of salaries, benefits and other privileges. If your case fall under this types of "transfer", you need to consult your lawyer.
On a practical note: if you bank has an existing union, you may ask for their assistance to negotiate mutually advantageous terms between you and your employer.