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.

If J.P. Morgan loses the lawsuit, it could be forced to take a $1 billion charge against earnings in the fourth quarter. A number of J.P Morgan executives are expected to testify during the three-week trial, including Marc Shapiro, the bank's vice chairman for finance and risk management, and Jeffrey Dellapina, a bank managing director.

During the earlier congressional hearings, Levin and other senators characterized the deals involving J.P. Morgan and Citigroup as "sham transactions." The lawmakers contend that the deals enabled Enron to mislead investors by reporting artificially inflated revenue and lower liabilities on its books.

Bank officials declined to comment on the newest hearing.

But it's clear that J.P. Morgan officials remain concerned about the potential for the company's dealings with Enron to stir up more negative publicity.

This week, on the eve of the trial in New York, William McDavid, the bank's general counsel, sent an email to the bank's employees telling them to expect to read some negative stories in the press about the bank over the next few weeks.

"As usual in litigation, our adversaries may try to confuse the jury with smear tactics such as taking phrases from documents that, when twisted or taken out of context, put us in a bad light or appear to support their theory," said McDavid in the email. "We hope you will also hear stories that go to the truth."