Every organization has its own transfer policy. I think in your appointment, the said clause regarding transfer might be there. Generally, management, which has multiple business centers, will transfer their employees from one place to another depending upon work exigencies. So, management has the right to do this. At the same time, the reasons for such transfers should be genuine and free from any act of victimization by the employer. In your case, whether the management's action in transferring you to a new place 900 KM away from your present location is genuine or not, we do not know.
Generally, in any company, lower cadre employees such as clerks, peons, watch and ward, and security guards will not be transferred from one place to another. Only higher cadre employees such as branch in charge, key accounts persons, or HR employees will be considered for transfer for various reasons. In your case, you have to consider these factors. How are your relations with management these days? Do you have a cordial relationship with your boss or supervisors? What about your job performance? Are you actively involved in union activities?
Even if you are unaware of the exact reason for your transfer, you should meet with your HR Department or your immediate boss and seek their help or advice in withdrawing the transfer order issued by management. Convince them by explaining the problems you are currently facing. If they consider your request favorably, that's good. Otherwise, the management's decision will be final, and if they transfer you for genuine work exigencies, you have no other option but to report for duty at the new location or consider quitting if it is difficult for you to relocate. In such a situation, you may request the management to extend the joining duty time at the new location while you search for another job in your current area and resign thereafter if you choose to do so.
However, you cannot challenge the management's decision if they transfer you for genuine reasons. Refusing to accept the transfer order may lead to departmental action based on insubordination, as per the provisions of the standing orders or service rules of the company, and they may terminate your services eventually.
Regards