In all honesty, if you don't have the employee fill out the W9, it will not harm you in any way, but if the person is an independent contractor, they are supposed to fill out the W9 to verify that backup withholding is not necessary. The reason I brought it up is because if you want to dot your i's and cross your t's, you should. Not doing it will not effect your business, but if you want to be thorough, is should be filled out. If you want to see where it is explained, backup withholding is explained in publication 505.