Viacom is challenging creatives to produce a long-copy 48-sheet poster using no fewer than 50 words of copy. The winners of the competition, which is called "Copywriting goes Underground", will have their poster executions displayed at 25 key stations on the London Underground network across a two-week period during the summer.
The media value of the prize is £25,000 and the winning creative team will also win a European city break and a cash prize.
Mike Baker, Viacom Outdoor's European marketing director, said: "There are some clients who use this medium incredibly well, but this is a chance for more clients and creatives to focus on the Tube's real strengths - long dwell time and inescapable scale."
All of the shortlisted entries will also go on display at the London Transport Museum gallery in Covent Garden, in an attempt to create an exhibition of the best of contemporary advertising copywriting.