At an event in New York billed as a major speech on Wall Street and financial policy, Sanders slammed Clinton's financial-reform plan.
He said Clinton was unnecessarily dismissing Sanders' proposal to separate investment and commercial banks, a return to the Glass-Steagall Act that split the two for much of the 20th century.
"My opponent, Secretary Clinton, says that Glass-Steagall would not have prevented the financial crisis because shadow banks like AIG and Lehman Brothers, not big commercial banks, were the real culprits," Sanders said to an audience at The Town Hall venue in midtown Manhattan.
He continued: "Secretary Clinton is wrong."
Sanders also took a subtle shot at Clinton's husband, former President Bill Clinton, noting that the Glass-Steagall Act was repealed during his administration. And he suggested that Clinton was part of an "establishment" culture not serious enough in its punishments of the culprits of the 2008 financial collapse.
"My opponent says that as a senator she told bankers to 'cut it out' and end their destructive behavior," Sanders said, pausing while the audience laughed. "But, in my view, establishment politicians are the ones who need to 'cut it out.' The reality is that Congress doesn't regulate Wall Street. Wall Street and their lobbyists regulate Congress."
The sharpening of Sanders' rhetoric comes as he continues to trail Clinton by somewhat healthy margins in most national polls of the Democratic primary.
The crowd at the venue - a mix of Communications Workers of America union workers, local lawmakers from New York and New Jersey, and many younger attendees - embraced Sanders' attacks on the former secretary of state.
When Sanders name-checked Clinton, scattered boos splattered through the audience. And when he twice declared that Clinton was "wrong," the audience erupted in applause.
In a lengthy speech that totaled more than 3,000 words, Sanders pledged to create a list of "too big to fail" institutions within his first 100 days in office. He also declared that he plans to break up the major financial institutions within one year of taking office.
Though it featured much of the same populist rhetoric as Sanders' usual stump speech, the senator incorporated a few more pieces of applause-ready zingers into his normal routine.
"Here is a New Year's resolution that I will keep if elected president," he quipped. "If Wall Street does not end its greed, we will end it for them."