Dear Felix
It is reasonable to expect our employees to fall ill occasionally and be unable to arrive at work. It is for this reason we extend [X] sick day leaves per year to each of our employees. Unfortunately, you have missed work for a total of [Y] days this year: [LIST DATES, ex. January 2, 12, 13, February 2, 3, 4, and March 1, 2, and 3].
This excessive use of sick leave days blemishes you history of good performance. Accordingly, additional sick leave this year will be unpaid.
If there exists a situation or underlying problem which we must discuss, I urge you to bring it to my attention so we can act accordingly. Otherwise, please contact me as soon as possible so that we may discuss the situation.
Regards
Lydia