Mr. Hitesh has given a good letter which you can use. However, here and there, I feel it to be a little harsh. An employer has to be firm but need not be harsh even in the worst situations. I suggest the following changes to his letter:
Instead of "Off and on," it would be better to use "frequently." Instead of "verbally," I feel it can be "orally." Instead of "are warned for improving," it could be "you have not shown any improvement." Instead of "no alternative," it might be "we would be constrained to take further appropriate action as deemed fit in the circumstances."
Please note these are my suggestions. I am not decrying Mr. Hitesh. The suggestions, according to me, would project the management in a better light. You may accept or reject them. It would be better to wait and get opinions from other fellow members in this regard and then make a wise and final decision.
Regards,
M.J. Subramanyam, Bangalore