U.S. federal energy regulators charged electricity traders at a JPMorgan Chase & Co. subsidiary which agreed to pay $410 million on Tuesday to resolve accusations that it manipulated electricity prices.

The Federal Energy Regulatory Commission, an independent agency that regulates the interstate transmission of electricity, oil and natural gas, said the Wall Street bank was using an "abusive" trading strategy that successfully forced the grid to recompense for plants to sit idle, ultimately accumulating to customers' costs. FERC said that the improper conduct happened between September 2010 and June 2011 in California, and three in the Midwest from October 2010 to May 2011. Late Monday they issued a formal "notice of alleged violations" against the investment bank.

The biggest U.S. bank, JPMorgan, is recompensing a civil penalty of $285 million and returning $125 million in apparently improper profits.

New York-based JPMorgan in a written statement said that it's "pleased to have reached an agreement with FERC to put this matter behind it." FERC spokeswoman Mary O'Driscoll failed to comment on the document or on possible penalties, as did JPMorgan representative Brian Marchiony.

FERC staff discovered that the bank "engaged in five manipulative bidding strategies designed to improperly obtain payments at above-market rates from the California Independent System Operator." The quasi-governmental company, based in Folsom near Sacramento, functions most of the state's electricity transmission grid.

There is an estimate of $63 million overpaid electric bills by California industrial, commercial and residential consumers

A year ago, FERC suggested that bidding practices in JPMorgan's commodities trading business "may have been designed to manipulate" the markets.

"Civil fines don't go to California. They don't go to working families. They go to the Treasury,"  Tyson Slocum, director of the energy program for Public Citizen said. "Who is making California ratepayers whole?"

The allegations against JPMorgan "are very similar to the kinds of shenanigans that Enron pulled," he said.