A simple version of this is that you are woking to the terms laid down in this contract which at the time of your employment beginning both you and your employer would have signed...this is a legally binding document and cannot be changed without both parties agreeing, so you can therefore quite within your rights refuse this amendment....However back in thereal world the point may well be that your job could be on the line if you aren't more flexible...Some points spring to mind straight away......Are the company offering any extra remuneration for the extra hours? Are you a member of any unions? Are there many other emploees in the same boat? If you do find yourself on your own my advice would be get yourself to the C.A.B. and ask them for help.