Mother and Wieden & Kennedy have been briefed to come up with a new definition for the Amnesty brand that will revitalise the organisation's profile at a time when it is under increasing pressure to achieve its targets and reach more people.
The two agencies have been asked to come up with a through-the-line strategy.
Amnesty uses a wide range of media to talk to consumers. It backs talks and concerts and employs celebrity ambassadors, rather than just purely advertising-led solutions.
A spokesman for Amnesty said: "The Amnesty brand already has enormous power and profile, but our work has never been more urgent. We have got to remain ambitious.
"Making the most of our brand is going to play a big part in this, which is why we're talking to agencies to help us deliver a creative idea that can make this country alive to the importance of what we do."
Amnesty does not have a retained agency, choosing to work with several different agencies on one-off projects.
Karmarama, the communications design agency, was recently appointed to create a campaign as part of a drive to stop violence against women. Catalyst works with Amnesty on direct marketing.