“I disapprove of what you say, but I will defend to the death your right to say it”
Warbler, laws protecting you at your workplace are different from laws protecting you from the government. If you routinely don’t come dressed appropriately for your job, you can get fired. If you make a public statement that potentially can make the company look bad and thus hurt sales, you can get fired.
The First Amendment gives the right to freedom of speech, association, assembly, and the press. It does not inherently protect you at your job. We do have laws (not amendments) in place to protect people from being fired based on race or gender, but that’s not this. And you would have to prove that was the only reason for the firing.
Having an opinion is one thing. Posting it in the newspaper is something else.