As a government employee you may have less freedom of speech rights than private sector employees.

But that's probably not relevant here. The concept of freedom of speech is about criticizing the government, publicly or privately. Your situation is different - you disagreed with a member of management at your employer. As I said before, employers are legally free to discipline their employees for disagreeing with their management staff. Whether said disagreement is expressed publicly or privately, rudely or politely, is not a matter addressed by law. You therefore have no legal recourse here. If you're a union member, you may have recourse with the union. But not outside that.

(And I really really hope for your sake that Michael Jones isn't your real name.)