Yes you can. A cease and desist letter is a request of another to stop a certain action in violation of a copyright, an agreement between parties, or otherwise infringes on the rights or property of others in some way. I am not an attorney, so there may be other reasons but those come to mind.
Your letter should be factual in nature and request they cease and desist from an action, give your grounds for the request, and indicate a failure to do so may/will result in your seeking legal recourse to protect your rights. As has been suggested, send it Certified Mail, Return Receipt Requested, and note on the letter that you have CC’d your attorney so they know you mean business.