1234, Main Street
Boston, MA 02123
<Recipient Address Goes Here>
As we discussed in our meeting <time of meeting>, <review topic of discussion>.
There often are extenuating circumstances that cause us to violate company policy from time to time, but when the behavior is frequent, it causes a hardship on co-workers and decreases overall productivity.
Please consider this a formal warning that this behavior can no longer be tolerated. We value our employees and if there is something we can do to help the situation, please let me know. In the meantime, I will expect you to <expectation>.
encl: <List of enclosed items goes here>