If an Organisation is shifting its complete Head office, from one location to another, with all government permissions, I don’t think you have any option to accept the transfer or not. Whatever may be the clause In appointment letter, when company itself is shifting, you have to accept the same. The message from your boss itself is wrong. He should not ask you, whether you want transfer or not. He should write, ‘you will be transferred’. (it is presumed that you are head office employee).
If at all, your Company has another office premises in Ahmedabad, where any of your other department is working, and your job profile suits to work in that department, you can request to Management, that you want to remain at Ahmedabad, due to some reasons (give few reasons which sound genuine).