A "written warning" is a formal notice given to someone when they have done something wrong or made a mistake. It is written down and serves as a reminder or a signal that if the behavior or actions continue, there may be further consequences.
They instead should have considered whether or not the decision was fair on the basis of how much emphasis was placed on the inappropriate final written warning. (mooreblatch.com)
Here are some tips that you may use in writing your warning letter. (template.net)
A progressive disciplinary plan involves providing the employee with written warning. (employmentlaw101.ca)