That doesn't rate firing, since he was implementing his boss's policy. Failing to resign over a treasonous policy is what rates firing.
From the article I read: The union was incensed when Morgan told a Senate hearing Dec. 1, in response to a question from Sen. Tom Carper, D-Del., that he supported a comprehensive immigration overhaul, which is often interpreted to include a path to citizenship for people who are in the country illegally. The guy claimed he was not for "blanket amnesty", but we all know what "comprehensive immigration overhaul" means. Trump probably talked to him and ascertained that he was another amnesty pusher and fired his ass.