This is an employment question.
I've retagged it.
www.court-martial.com; www.court-martial.us.com; firstname.lastname@example.org 703-298-9562, 800-401-1583. Answering your question does not create an attorney-client relationship.
In at will employment states, an employer may fire an employee for any reason, or no reason--so long as it was not anchored in discrimination (race, religion, gender etc.) or other illegal practices. I am NOT an Iowa attorney, but I recall that IA is an "at will" employment state.
The Constitution protects you from the government attempting to quell your speech rights--not employers..
See an employment attorney ASAP. To determine if you have any union or other procedural privilieges.
READ THIS BEFORE CALLING OR EMAILING ME: I am licensed to practice before the state and federal courts in Virginia. We have not established an attorney-client relationship unless we have a signed representation agreement and you have paid me. I am providing educational instruction only--not legal advice. You should speak with an attorney to whom you have provided all the facts, before you take steps that may impact your legal rights. I am not obligated to answer subsequent emails or phone calls unless you have hired me. I wish you the best of luck with your situation.
To fill in one point here -- I assume you're not a government employee. The First Amendment prohibits only the government from restricting free speech. It does not keep private companies or individuals from restricting free speech and specifically does not prohibit private employers from restricting the free speech of their employees. That's why you have an employment issue and not a constitutional issue.