A dispute over shadow banking is heating up between Bernie Sanders and Hillary Clinton as the Democratic presidential hopefuls sharpen their messages to voters ahead of the first votes of the 2016 presidential campaign.

Sanders, a Vermont senator, is slated to give a speech on Wall Street reform Tuesday afternoon, in an attempt to cast himself as the industry’s toughest cop — and to rebut criticism from Clinton’s campaign about his policies.

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Sanders will reportedly say the reinstatement of the Glass-Steagall Act would aim to crack down on the so-called shadow banking system — which operates outside government bank regulators’ jurisdiction. Shadow banking refers to lending outside the banking system. Such lending can come from institutions including hedge funds, private-equity firms and money-market funds.

The International Monetary Fund blamed shadow banks — entities it says have little supervisory oversight and weak governance — for contributing to the global financial crisis in 2008. The Financial Stability Board, which was created by the Group of 20 nations, recently found the U.S. accounted for 40% of global shadow-banking assets in 2014.

Clinton opposes reinstating Glass-Steagall, which separated commercial and investment banking. And her campaign is saying Sanders doesn’t go far enough in addressing some of the biggest culprits of the 2008 crisis.

In his speech, “Sen. Sanders should go beyond his existing plans for reforming Wall Street and endorse Hillary Clinton’s tough, comprehensive proposals to rein in risky behavior within the shadow banking sector,” Clinton’s chief financial officer Gary Gensler said in a statement on Monday.

A Sanders spokesman shot back: “Sen. Sanders won’t be taking advice on how to regulate Wall Street from a former Goldman Sachs partner and a former Treasury Department official who helped Wall Street rig the system.”

The newest round of sparring between the Democratic rivals comes just weeks before the Iowa caucuses and the New Hampshire primary, the first two voting contests of the 2016 race. Clinton is comfortably ahead of Sanders in a recent average of Iowa polls, but he leads her in New Hampshire.

Clinton has said she would make the shadow-banking sector more transparent, and impose margin and collateral requirements on certain securities financing transactions.

The campaign of former Maryland Gov. Martin O’Malley, who is trailing both Clinton and Sanders for the nomination, said Sanders doesn’t go far enough in his proposals.

“But he certainly goes farther than the so-called ‘weak tea’ she has proposed,” said Lis Smith, O’Malley’s deputy campaign manager, in a statement. “Secretary Clinton’s proposals have actually been welcomed by Wall Street because they would let big banks ‘off the hook.’”