E.On, which was hit with a record £12m fine for mis-selling earlier this year, is understood to spend more than £250,000 per year on comms with the two incumbent agencies.
It claims to rank around third in the energy market, with five million business and residential customers.
London-based 3 Monkeys handles its consumer, corporate and B2B communications while Manchester-based Tangerine PR covers regional media relations.
The latter, which was appointed in 2012, is to repitch, but it is not clear whether 3 Monkeys, which was appointed in 2010, will also participate.
Scott Somerville, press office manager for E.On, confirmed the company had made approaches to agencies.
"We’ve taken the decision to take a fresh look at our PR agency support," he said. "We’ve had very successful relationships with 3 Monkeys and Tangerine PR and both agencies have delivered good results for us.
"Energy remains high on the media and political agenda, and the time is now right for us to review our activities in order to ensure we continue to meet our primary objective of becoming our customers’ trusted energy partner."
Tangerine PR consumer MD Mary Harding said: "We’ve had a very successful partnership with E.ON, working closely with the in-house PR team to engage and educate local communities on how they can use no more energy than they need.
"We’re very excited at the prospect of developing our recommendations for a fully integrated campaign plan."
E.On's public affairs needs are not part of the review, as they are handled by its in-house team.
3 Monkeys declined to comment.