Declining a job offer after you have accepted an offer letter is a serious matter. Harvard University calls it an "egregious breach of ethics" that could damage your professional reputation. The University of Pennsylvania maintains doing so could ruin your chances of ever working for the organization making the offer -- or at similar companies. The universities maintain that you should follow through on accepting the job, unless there is an extreme reason not to. If you must decline a job offer after accepting, you should do it with as much professionalism as possible.
Review your reasons for wanting to back out. Some reasons are more understandable for employers than others. Backing out because you received a better job offer at the last minute is unethical, according to Northern Illinois University, but the hiring manager may understand other reasons. During your review, decide one last time if backing out is what you really want to do. If necessary, get advice from a mentor before reaching a final decision.
Call the hiring manager or human resources representative who sent the job offer letter. The company considers your hiring a done deal once you formally accept the offer letter. If you are backing out, you owe the company the courtesy of a telephone call instead of an email or letter.
Tell the truth. Get right to the point at the start of the conversation as you apologize for flip-flopping. Explain why you are pulling out. Tell the representative about a better job offer, concerns about a spouse who is reluctant to move, or feelings of guilt about leaving aging parents. Hiring managers and human resource representatives are human too. They understand how life events can change things -- although they are sure to be upset if you're backing out to take another job.
Even if you're unsure about the job, it may be better to take the position and work there at least a year. By then, even more job opportunities may be available to you, and you would not have burned bridges by backing out on your original offer.
Backing out on a job offer could reflect badly on your university if you are a graduating senior. Universities take great pride in developing students who stand on their word to potential employers. For example, Duke University has a policy of possibly suspending employers from recruiting on campus if they make a habit of rescinding job offers. In turn, Duke expects its students to honor their commitments, as well.