The move follows the arrival of Jeremy Davies from the Santander-owned bank Abbey as the new director of brand and communications.
TBWA was appointed to the business in 2007, and has produced a series of brand and retail campaigns for E.ON, as well as activity to support its FA Cup Sponsorship. Powergen rebranded as E.ON in 2007.
E.ON said it now intends to "hone its communications strategy for 2009 and beyond", and as a result the decision has been made by Davies, along with head of advertising and communications, Catherine Woolfe, to conduct the review.
The review is being conducted by Agency Insight.
The £30m media planning and buying account, which includes online, is unaffected by the decision. It moved in August of this year from Initiative and Zed Media to MediaCom.
According to Nielsen adspend figures, E.ON spent £20m on advertising in the 12 months ending September 30, 2008. E.ON is expected to reduce its adspend in 2009, a source said.