The Federal Energy Regulation Commission (FERC) monitors the electricity, gas and oil markets in the US, with a particular focus on the wholesale side.
That means it regulates sales, reviews merger and acquisition activity in the sector, and monitors market and trading activity – the final point covering the accusations levelled at Barclays.
FERC was set up 35 years ago, but came into its own in 2005.
The agency was given much greater powers to go after suspected market abusers in 2005 following the California power trading scandal and the collapse of Enron.
It wants to levy a $435m (£270m) civil penalty on Barclays, as well as $349m in gains from the alleged manipulation and interest on those gains. That is far in excess of the $245m settlement the agency reached with Constellation Energy at the start of 2012, its biggest claim to date.