BBDO West, Los Angeles, which won the account three years ago, is not going to participate, a spokesperson said.
Mitsubishi said it's in the final few weeks of a contract with the Omnicom Group shop.
"BBDO West has been instrumental in the revitalization of the Mitsubishi brand in North America," Dan Kuhnert, exec VP-sales and marketing, said in a prepared statement. "However, as Mitsubishi Motors begins a new three-year plan globally, it is appropriate for us to consider new possibilities."
According to BBDO, the review affects only the U.S., and its Toronto office will continue to handle Mitsubishi in Canada.
Omnicom's PHD, Los Angeles, still has U.S. media and is not part of the review.
The automaker, which hit the financial skids several years ago after overly generous incentives, saw its U.S. car sales increase last year nearly 8% over 2006 to 128,993 vehicles.
The marketer will hire Selective Resource International to handle the review, with requests for proposals going out in the next couple of weeks, the spokesperson said. Mitsubishi expects to complete the process by June 30.
Mitsubishi spent $155 million in U.S. measured media in 2007, according to TNS Media Intelligence.