It is interesting for a targeted campaign like this administration's—which claims to be concerned with government waste and inefficiency—to cut employees for one of the only organizations that we know causes decreased revenues for the federal government when it receives cuts in funding [1].
Of course, it's not like they're implementing any sort of new policies to make sure productivity in the IRS remains the same. I'm not sure why we'd expect anything less at this point.
Insofar as you're tariff-ing everything that moves, the less you particularly care about internal revenue. The endgame is to eliminate the income tax entirely anyway, so why would one want the IRS at all?
A separate, connected thought is that I wonder why you would choose being a federal employee then. Here, the government promises job security but it usually means less pay and slower processes compared to industry. If you don't have job security, is then the government forced to be more competitive with industry positions in pay/processes?
That said, the current regime has had no problem acting outside of the law and existing federal employee union contracts. Tell people they're dismissed, cut off the email and building access, wait for the lawsuits, and then simply ignore the decisions weeks/months later and/or follow them with as much malicious compliance as they need to achieve their original aims.
tl;dr: No, employment protections fundamentally don't exist in the US, and doubly so for those employed by the federal government within an atmosphere of rampant lawlessness.