I am resigning from my current organization. My last working day is 22 Oct 2016, but now a new clause is added to my resignation acceptance that "by signing this letter you accept that you are not going to join any business competitor for the next 6 months." Can a company add this type of clause at any point in time? I do not accept this letter and refuse to sign as I am going to join the same line of business with other organizations. Please suggest what to do.