The company, which has artists on its roster including James Blunt, Muse and the Red Hot Chili Peppers, has kicked off a review across its various music labels.
PHD, which was appointed a year ago to handle the vast bulk of the business, has declined to repitch for the task.
Warner has approached at least two non-roster agencies about the business. It is using the consultant Charlie Thelu, a former vice-president of global purchasing at EMI, to co-ordinate the process.
The pitch follows the recent appointment of the Warner marketing director, Greg Castell, and comes amid a testing time in the record industry as music downloads are increasingly threatening sales.
Warner's advertising spend has dramatically decreased as it looks at alternative ways of marketing its artists. Warner's record labels include Warner Brothers, Atlantic Records and East West.
PHD handles planning and buying across the main brands such as Warner and Atlantic.
Earlier this year, Warner approached EMI over a potential merger, but a deal failed to materialise. EMI was eventually acquired by Terra Firma, the private equity vehicle run by Guy Hands.
Castell was unavailable for comment.