Human Resource, Payroll & PEO Information At APR, we strive to provide our clients with up-to-date information and valuable resources so that they can be sure they are making the right choices for their small businesses. National Association of Professional Employer Organizations The NAPEO is the largest trade association for PEOs. Internal Revenue Service Get access to forms, tools and tax resources. U.S. Department of Labor Find the information you need to keep your business compliant. Society For Human Resource Management The world's largest HR membership organization. American Payroll Association The nation's leader in payroll education, publications and training. Federal Tax Identification Number Register for a Tax Identification Number (EIN).