There are many reasons why your employer may rescind a job offer. You may have failed a drug test.Be polite, don't make up reasons. Just tell them you regret to inform them that you can't take the position. Learn what a withdrawal letter is, how to write a letter of withdrawal and see a template and an example to help you write your own. I've rejected two separate offers from two separate times in my "work" life for two separate reasons. The first I didn't feel any remorse. Draft a formal rescission letter. Send them a physical letter that includes the information that was provided over the phone. This is an informational list of forms for individuals considering a change in job status.