The U.S. Federal Energy Regulatory Commission (FERC) ordered Barclays and four of its power traders to pay fines totaling $453 million on Tuesday, saying the bank manipulated California's electricity markets last decade.

The fine, first proposed in October 2012, must be paid within 30 days, FERC said on Tuesday.

Barclays has contested FERC's findings and has previously said it will fight the order in court.

(Reporting by David Sheppard and Matthew Robinson; Editing by Jan Paschal)