FERC said that Barclays manipulated electricity prices and reaped unjust profits in doing so.
The alleged manipulations, FERC said, took place in Arizona, Washington, Oregon and California from November 2006 through December 2008. Four of Barclays' traders, Daniel Brin, Scott Connelly, Karen Levine and Ryan Smith, now no longer with the bank, were named by FERC in separate suits of $1 million each.
In August 2013, Barclays refused to pay the $453 million in civil penalties FERC ordered the company to pay in July 2013. Barclays said it would fight FERC's allegations in court.
FERC ordered the fines based on the authority of the Federal Power Act and FERC's own Anti-Manipulation Rule.
Barclays has said that FERC's fines are "overstated and unjustified" and "unsupported by either the facts or the law."
Barclays has not traded in Western U.S. energy market since 2011.
FERC has also sought penalties from BP (almost $29 million) and J.P. Morgan Ventures Energy Corp. ($410 million). BP said the allegations were "without merit."