The purpose of Wisconsin’s Fair Employment law is to protect the rights of people to employment free of unlawful discrimination.  As a result, tt is unlawful, for public and private employers, employment agencies, licensing agencies and unions, to refuse to hire, to discharge, or otherwise discriminate in any term or condition of work, because of a persons protected class. 

Protected classes can be found here: http://www.dwd.state.wi.us/er/discrimination_civil_rights/publication_erd_6160_pweb.htm#5.