“I keep forgetting that you’re still alive,” the Tesla owner tweeted on Sunday morning.
Mr Musk’s tweet was in response to a tweet from the 80-year-old senator that demanded “the extremely wealthy pay their fair share. Period.”
While Mr Sanders has not responded yet, the world’s richest person proceeded to shoot off more tweets.
“Want me to sell more stock, Bernie? Just say the word…” the 50-year-old tech tycoon, who is also the owner of SpaceX, said in another tweet. Responding to a tweet by a user, Mr Musk again took aim at the politician. “Bernie is a taker, not a maker,” he said.
Mr Musk, who had become the richest person in the world with a current estimated personal wealth of $271bn (£201.6bn), was called out by Twitter users who said his tweet was “excessive” and “inhumane”.
“What a deeply offensive thing to say,” author and political activist Marianne Williamson said.
Mr Musk’s tweet was also described as “gross and inhumane” by writer Shaun King.
Author Molly Jong-Fast said: “This is so excessive.”
Hollywood actress Patricia Arquette replied to his tweet, asking: “Short term memory issues?”
Economist David Rothschild said “every billionaire owes massive debt to security, human capital, infrastructure, democracy that made their fortune possible.”
Brian Altano, a video producer, said Mr Musk could “even pay a little every month, like how you pay your child support.”
The chief executive’s efforts to pick a fight with a politician is his second such attempt in recent weeks. Earlier, he had hit out at Ron Wyden, the chairman of the senate’s finance committee, with another crude tweet.
“Whether or not the world’s wealthiest man pays any taxes at all shouldn’t depend on the results of a Twitter poll,” Mr Wyden had said.
“Why does ur [profile picture] look like u just came?” Mr Musk had shot back.
Mr Musk does not receive a salary from Tesla but is instead required to pay taxes on gains. This means that even as his net worth rises through his holding of Tesla stocks, he does not have to pay taxes on any unrealised capital gains.
Mr Sanders, a Vermont independent who caucuses with Democrats, is also the chair of the senate’s budget committee. He has been advocating a “billionaire tax” that would tax these unrealised capital gains.
Mr Musk offloaded nearly $7bn (£5.2bn) shares of Tesla over the past week following an unusual poll on 7 November on Twitter, in response to the billionaire tax, asking followers whether he should sell the shares.
“Note, I do not take a cash salary or bonus from anywhere. I only have stock, thus the only way for me to pay taxes personally is to sell stock,” Mr Musk had said.
His wealth had dipped by $50bn (about £37bn) two days after the poll.