Check the format attached of Late Coming Memo it may be helpful for you.
Name and address of employee to whom warning is being given
Subject: Warning letter
Dear Ms/Mr __________
We have given repeated verbal warnings to you regarding coming late to office every other day. The management has noticed that no heed has been paid to those warnings. So we are writing this warning letter to you. You are requested to strictly start following the office timings with immediate effect failing which we will be compelled to start deducting a day’s salary for every day that you come late to work.
Please sign a copy of this letter in acknowledgement of receipt of this letter.
Hope to see you complying with the company rules.
(Name of signing authority)
Please note that coming late to work affects not only your work it affects the entire process you are involved in.
You are here by advised to be punctual to work .