Federal employment law doesn't ban discrimination based on political affiliation. A minority of states ban discrimination based on political activity:

• Some states ban firing based on "political activity," including California, Colorado, Louisiana, Minnesota, Missouri, Nebraska, Nevada, South Carolina, Utah, and West Virginia. Cities like Seattle and Madison fall on this list, too.
• Montana also bans firing absent good cause, which would protect political activity.
• New Mexico bans firing based on "political opinions."
• Statutes protect belonging to a political party in D.C., Iowa, Puerto Rico, and the Virgin Islands. This also includes Broward County (Fl.) and Urbana (Il.).
• Colorado and North Dakota ban firing based on off-duty lawful activity (including speech), while Connecticut protects employees from retaliation for speech broadly.
• Illinois, New York, and Washington have laws that apply to election-related activities.
• Hawaii, Idaho, Kentucky, Tennessee, West Virginia, Wyoming, and Guam ban retaliation for petitions or voting.