Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [name of rep in compliance or legal],
I would like to make a confidential complaint regarding [detail of issue here]. I have witnessed this activity, and am completely uncomfortable with the legal and ethical ramifications associated with it.
I have brought this issue to my immediate supervisor, but I don't feel that it has been appropriately addressed or taken care of, as it appears that the issue is still present.
I do not want to get anyone in trouble or cause an issue, but I feel like this type of activity could negatively impact the company and should be looked into and appropriately addressed.
Thank you so much in advance for reviewing this situation, and for keeping my report confidential.