NEW YORK: The long march back into the black at the world's third largest agency holding company took an abrupt backward step on Tuesday as Interpublic Group's largest client, General Motors, withdrew two of its major brands - GMC and Buick.

The brands, which between them represent an annual $400 million (€297.77m; £200.35m) in billings and $30m in revenues, have defected to Publicis Group's Leo Burnett in Chicago. Although their departure is a major blow to IPG's recovery plan, GM remains its largest client.

The Buick creative business was handled by McCann-Erickson, while GMC abided with Lowe Worldwide. Insiders say layoffs are inevitable and the decision could even result in the closure of McCann's Detroit office.

The withdrawal of the GM duo is a double whammy for the ailing agency conglomerate, which last week bade farewell to several major Johnson & Johnson brands. Its remaining J&J business is currently under review with a decision said to be imminent.

Interpublic chairman/ceo Michael Roth (above) did his best to put a brave face on the situation: "We're proud of the work our agencies are doing for this important client and of the fact we remain GM's largest provider of marketing services," he said. "We look forward to continuing to play a key role in GM's future success."

Data sourced from Wall Street Journal Online. additional content by WARC staff