Citigroup ( C) and J.P. Morgan ( JPM) will be on the hot seat again on Capitol Hill over their business dealings with Enron. Earlier this summer, a Senate subcommittee held several high-profile hearings that explored the role both banks played in arranging questionable financing deals for Enron involving so-called prepaid oil and gas contracts. The hearings, during which lawmakers accused the banks of helping Enron inflate its earnings, created a tidal wave of negative publicity for Citigroup and J.P. Morgan and contributed to a fierce selloff in the banks' stocks. And now lawmakers seem poised to tackle the potentially embarrassing subject one more time, sources say. In a surprise move, Sen. Carl Levin (D., Mich.), the outgoing chairman of the Senate's Permanent Subcommittee on Investigations, has scheduled another all-day hearing on Dec. 11 to look into the deals between the two big banks and Enron. Sources say that in the past few days, Levin's office has notified both banks that some of their employees who worked on the financing deals may be asked to testify. In addition, the panel intends to call a number of securities regulators as witnesses. The panel may release a list of witnesses on Friday. The timing of the latest hearing could be particularly problematic for J.P. Morgan, which is in court right now trying to defend those very same deals. Earlier this week, a federal jury in New York began hearing testimony in J.P. Morgan's quest to force a group of 11 insurers to honor a $1 billion insurance policy it took on $3.7 billion in prepay deals with Enron. The insurers are refusing to pay the $1 billion, claiming that the deals between J.P. Morgan were really "disguised loans," and not true contracts to buy and ship oil and gas supplies. J.P. Morgan, meanwhile, contends the insurers knew how the deals were structured and are simply looking for an excuse not to pay the bank.