The moves are said to be financially based, as GM figures ways to cut costs in the tough U.S. market.
A Starcom spokeswoman confirmed that the media accounts will transition to the two agencies in the next three months, but she said she didn't know which car brands were moving to which shop. She also said she believes the move involves both planning and buying of media.
Starcom has about 100 staffers currently handling GM's regional dealer media accounts, said two executives close to the matter who asked not to be named. The regional dealer groups have historically spent hundreds of millions of dollars in advertising annually.
Martin Retail already handles Buick-Pontiac-GMC's regional dealer creative account; Velocity has the bulk of Chevrolet's regional dealer ad group business.
A GM spokeswoman declined comment. David Martin, president of Martin Retail, didn't return calls. Neither did Mark LaNeve, VP-sales-service and marketing for GM in North America, or Ed Peper, VP of Chevrolet in the region.