Story highlights The Glass-Steagall Act was a Depression-era law passed that separated commercial and investment banking

The reinstatement of the law has become something liberal leaders have championed since its repeal

Washington (CNN) Massachusetts Sen. Elizabeth Warren pushed for the reinstatement of a major Depression-era banking law on Wednesday, emailing her large list of supporters to push for the measure.

The plea from the progressive icon comes two days after an economic adviser to Hillary Clinton's campaign said the presidential candidate wouldn't reinstate the Glass-Steagall Act if elected.

"Wall Street spent decades -- and millions of dollars -- to repeal the original Glass-Steagall Act, and you can bet they'll do whatever it takes to keep it from being reinstated," Warren wrote in an email titled "Let's get real." "We need grassroots support from all across the country if we're going to fight back to make our financial institutions smaller and safer."

The email asked supporters to sign a petition supporting Warren's "21st Century Glass-Steagall Act," which was introduced by the senator -- along with Republican Sen. John McCain -- last week.

The Glass-Steagall Act was a Depression-era law passed in 1933 that separated commercial and investment banking. The law was in place for more than 60 years until President Bill Clinton, with the backing of Congressional Republicans, repealed the law in 1999.

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