Elon Musk's email ultimatum directing federal workers to justify their job positions is nothing but a scam the American public can see right through ... so says a top Democratic senator.

The U.S. Senator from Minnesota, Tina Smith, joined us on "TMZ Live" Monday -- branding Elon as nothing but a bully using his power to be a jerk, labeling his actions as downright harassment.

Catch the video ... 'cause we pointed out it seemed like the White House seems to revel in the outrage over Elon's latest power play -- and she made it clear that's definitely the case.

ICYMI, Elon sent an email to every single federal employee Saturday afternoon demanding each worker reply with five bullet points recounting what they accomplished at work the previous week ... and later tweeted a failure to reply by midnight Monday would be considered a resignation.

Smith dives deeper into her outrage, blasting Elon for gleefully wielding his power to make people's lives miserable … calling it the ultimate example of an unpleasant, petty boss.

Tina says despite Elon's attempt to tear down the federal accountability system that keeps billionaires like him in check, Americans see right through the act.

Bottom line ... Tina says Elon might think he's untouchable, but the public knows what he's up to -- and the tidal wave of support behind her proves the fight's just getting started.

Watch "TMZ Live" today ... check your local listings.