A sudden $2 billion trading loss at banking giant JPMorgan Chase & Co. prompted two Senators to renew their calls for regulators to toughen the implementation of rules aimed at cracking down on risky bank bets.

The proposed Volcker Rule mandated by the Dodd-Frank financial reform law would limit banks’ ability to bet on markets with their customers’ money. Democratic Sens. Jeff Merkley (Ore.) and Carl Levin (Mich.) have been pushing regulators to stiffen their draft language on the rule and pointed today to the $2 billion loss — which happened over just a few weeks — as fuel for their argument. JPMorgan announced the major loss in a conference call Thursday evening, according to reports.

Levin criticized JPMorgan CEO Jamie Dimon as someone who doesn’t want derivatives to be regulated, doesn’t want the Volcker Rule and wants the ability to escape regulations by trading in London.

“Those positions of his have dramatically proven to be wrong,” Levin said on a conference call with reporters

Levin and Merkley said the draft regulations implementing the law have a huge loophole called “portfolio hedging” that undercuts the point of the law.

“This is a matter of whether the law is going to be abided by, first by the regulators and then by Wall Street,” Levin said.

The risk is that a major bank will fail and drag down the economy with it, the two said.

“When big investments blow up, it can take down a bank,” Merkley said. If a bank like JPMorgan failed, “it would have a very substantial impact on markets across this country and institutions across this country.”

And in light of the losses, “regulators have absolutely no excuse to create the loophole that they had in the draft,” Merkley said.

Levin also took a whack at presumed Republican presidential nominee Mitt Romney. “We’ve got a candidate for president who wants to wipe out the whole law,” he said. “He doesn’t just want to create a loophole, he would repeal Dodd-Frank, which would remove the possibility that we would have a cop on the beat.”

Levin said it’s too early to say whether he will hold hearings or otherwise probe the loss but that the Securities and Exchange Commission should take a look at the bank’s financial filings.