U.S. senators preparing to hear testimony from JPMorgan Chase ($52.30 1.33%) CEO Jamie Dimon said they will press him to explain what led to more than $2 billion in trading losses and will be looking closely at whether they need to tighten exemptions in the so-called Volcker rule, Bloomberg reported Wednesday morning.

U.S. Senator Jeff Merkley, D-Ore., is pushing for stronger restrictions on banks’ bets with their own money through proprietary trading. He said JPMorgan took too much risk.

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