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.

The Washington Post's Eugene Volokh did a deep dive on this topic, looking at political speech rights and where you can get fired for it.

Why it matters: "The First Amendment applies only to government employers; it doesn't apply to nongovernmental entities (whether or not those entities have government funding or contracts)," per Volokh.

What it means: If someone is fired on these grounds, these laws would all "likely authorize civil lawsuits," Volokh writes. And the First Amendment keeps all of this in the balance since it is possible it would preempt any claims that political speech creates a hostile work environment, protecting the person who participated in political speech.

Caveat: Most employment is "at-will," meaning an employer can fire an employee for whatever reason, so long as it isn't forbidden by a statute.