The move is believed to be part of an efficiency drive by the automotive giant to combine its back-office operations, including marketing.
The consolidation is in keeping with the company's decision to centralise its £98m media accounts for Vauxhall, Saab and Daewoo into Initiative last September.
Draft and TBWA\GGT have worked on the accounts for more than five years.
Saab is one of Draft's flagship accounts. Draft's recent work for the marque includes a mailing to 10,000 Saab owners in an attempt to convince them to repurchase the car.
DLKW Dialog, the below-the-line arm of Delaney Lund Knox Warren & Partners, which handles Vauxhall's above-the-line account, has also created some below-the-line projects for Vauxhall, mostly digital.
These include an interactive TV campaign for Vauxhall's 100th birthday. The agency is expected to attempt to secure a slice of the business now under review.
No one at GM was available to comment on the details.
It is not yet clear whether GM will look to consolidate Vauxhall and Saab's above-the-line creative. Vauxhall's creative account is currently split between Lowe and DLKW. Lowe handles Saab and Daewoo is with DFGW.
DLKW has made in-roads into Lowe's grip on the account in the past 12 months and now handles advertising for key brands including Corsa and Astra.
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