Does writing a poetic letter to one's employer that includes negative allusions about the company's manager constitute forbidden backbiting (Gheebah)?

Originally, backbiting is forbidden, and the Sharia (definition) warned against it. It is "your mentioning of your brother with what he dislikes." The Sharia has only permitted backbiting out of necessity, such as to remove injustice and to warn against evil. If the manager is bad, he should first be advised. If the advice does not work, it is permissible to report him to the company owner, mentioning only what is necessary to achieve the benefit and avoid harm. This is not considered forbidden backbiting.