[teraflop]

As a general rule, the First Amendment only restrains the government. It means the government can't ban speech (except in narrow, "content-neutral" ways) and courts can't punish you for it (except for things like defamation).

But the US follows at-will employment, under the more general principle of freedom of association. An employer does't have the same duty to treat its employees "fairly" that the government has to its citizens. Your employer can fire you for pretty much any reason, including differences of opinion, and the First Amendment has nothing to do with that.

The exceptions to this rule are better thought of as exceptions to at-will employment, rather than extensions of First Amendment protection. For instance, you can't fire an employee for discussing wages or working conditions with their co-workers, in the same way that you can't fire someone for being the wrong religion or for reporting illegal behavior.

(If you're saying that the courts should change their interpretation of the First Amendment to include a right to discuss politics at work... well, that would be a major break with precedent, and a huge reach beyond what the text of the amendment says, with wide-ranging ramifications. Instead, some states have passed specific laws that protect workers from discrimination on the basis of political opinion, without needing to invoke the First Amendment.)