Depending on your company's policy, they may pay you a per diem if you are working a temporary assignment in the field that is away from your regular work location and that requires you to stay overnight. This pay can be tax free to you if the assignment is temporary (intended to last less than 1 year). But there is no rule that a company must pay its employees a per diem. So talk to your boss or HR department and find out what the company policy is regarding per diem pay.