Dear Mr./Mrs. (name),
It was reported by your concerned Station In-charge (Higher Authority) that you had committed an offense of getting late for duty on (date). You must have known that it is a clear violation of service rules. (Describe in your own words). You were given the opportunity to clarify above-said act of violation but you did not bother to submit reply in your defense. (describe your requirement).
However, having seen your previous record and seniority, you are given one last chance to improve yourself and this time a Warning is imposed upon you so that you may realize the importance of arrival in time for duty. (Describe actual problem and situation).
Furthermore, you are directed to report to (Concern Person name) for completing pending tasks from your side.