The Nevada Democrat -- and frequent Trump foe -- levied the charge on Twitter, evoking a similar claim he made against the GOP's 2012 nominee, Mitt Romney.
"Trump is faking his net worth. He's not as rich as he would have us believe + a bad businessman. That's why we can't see his tax returns," Reid tweeted.
Reid, citing an unnamed source, memorably accused
Romney during the 2012 race of going 10 years without paying federal income taxes. Romney released a 20-year summary of his tax liabilities from 1990 through 2009, and his tax returns from 2010 and 2011. But he did not release additional returns.
The Trump campaign did not return CNN's request for comment.
Reid on Tuesday then went to the Senate floor to rip into Trump.
"The last thing the American people want or need is a president who will run another financial scam on each of them," the Nevada Democrat said. "If elected, Donald Trump would be the scammer in chief. Trump is a fraud."
"He's always looking for a mark, some victim for one of his schemes," Reid added. "And now our country is Trump's next target. He wants this to be his biggest payoff ever."
Reid's speech focused what he sees as lies about Trump's money and said the real estate mogul is only wealthy because he was born with "a silver spoon." Trump's father was a wealthy real estate magnate who loaned his son money
to jumpstart his career.
"Litigation is nothing new to Donald Trump. Over the last decade and a half, Trump and his companies and have been sued in federal court 72 times. That doesn't take into consideration the many times he's been sued in state courts," Reid said. "But Trump being the flim-flammer he is just moves on to another scam."
Reid, who is supporting Hillary Clinton, has repeatedly attacked Trump this campaign. Following Clinton's pneumonia diagnosis earlier this month, Reid attacked Trump's health.
"Take a look at this character that's running for president. He complains about her health. What does he do? He's 70 years old. He's not slim and trim. He brags about eating fast food every day. Look at his health a little bit," Reid said
And on Thursday, Reid tore into Trump
on the Senate floor, calling the Republican presidential nominee a "spoiled brat," "a con artist" and a "human leech who will bleed the country."