My name is _______ (name), working as a __________ (designation) in ___________ (department).
I write this email in reference to the task assigned to you on date __/__/____ (date). It has come to my attention that you have not submitted the _______ (project/monthly report/other) for the month of ______ (mention month). Also, the work you have done so far is not satisfactory and is below our expectation level.
I believe that you have the ability to give a better performance and I hope that you will improve your work productivity. If you ignore this, I will have to take the necessary actions against you. If you wish to discuss this matter further, you can contact me at _________ (contact details).
___________ (Employee ID Number),
___________ (Contact Details)