The Federal Energy Regulatory Commission's beefed up effort to crack down on alleged manipulations in the energy market is creating headaches on Wall Street and billable hours at large law firms. With this week's record fine against Barclays plc—and an even bigger settlement reportedly looming with J.P. Morgan Chase & Co.—it's shaping up to be a busy summer for lawyers at multiple firms, including Skadden, Arps, Slate, Meagher & Flom; Cadwalader, Wickersham & Taft; and Sutherland Asbill & Brennan.

As was widely reported Tuesday, FERC hit Barclays with a whopping $435 million penalty and fined four of its traders a combined $18 million for alleged manipulations of electric energy prices in California and other western markets. FERC also ordered Barclays to disgorge $34.9 million in unjust profits, plus interest, to low-income home energy assistance programs in Arizona, California, Oregon, and Washington.

The British bank vowed to contest the fine in a statement, insisting that it had done nothing wrong. According to people with knowledge of the matter, John Estes III of Skadden and Paul Pantano Jr. of Cadwalader will be leading the continuing fight for the bank, likely in the form of a declaratory action or a FERC enforcement proceeding in federal district court.

JPMorgan, meanwhile, appears ready to make a deal. The Wall Street Journal reports that FERC and the bank were exchanging drafts this week of an agreement that would result in the bank paying hundreds of millions of dollars—including a fine that would eclipse the one levied against Barclays. FERC's case against JPMorgan involves allegations that the bank manipulated energy markets in California and the Midwest.

FERC's investigation of JPMorgan has roped in lawyers from at least three firms since 2012. Catherine Krupka of Sutherland Asbill and a team at Skadden that included Estes and partners Michele Roberts and William Scherman represented the bank in U.S. district court for the District of Columbia in a discovery spat related to FERC's case. In November, the bank successfully fought off a subpoena to produce emails it deemed to be privileged. Scherman moved from Skadden to Gibson, Dunn & Crutcher in March of this year, and in May Gibson Dunn's Miguel Estrada appeared before the U.S. Court of Appeals for the D.C. Circuit to fend off FERC's appeal in the subpoena litigation.

Lawyers involved in both the Barclays and JPMorgan cases declined to comment.