You can never be forced to do anything. However, should you refuse and there is a valid financial reason for the transfer, you could find yourself being retrenched. The employer would have to go through all the procedures as set by law. They can only refuse to pay severance on the grounds that you refused reasonable alternative employment. What would be reasonable would depend entirely on the circumstances of the case BUT in your matter it would probably be seen as unreasonable to relocate to Cape Town.