You are never required to file an SS-8. You do not have to file one if you agree that you are a contractor, not an employee, or if you are satisfied to be treated as a contractor even if you think you should be considered an employee. You only have to file an SS-8 if you want the IRS to determine whether you should be treated as a contractor or an employee. It's up to you to decide whether you want to file an SS-8 or not. Be aware that filing an SS-8 might get the employer annoyed, which could result in losing the job.