In filings with the Securities and Exchange Commission, Interpublic said it will sell 9.5 million shares of Modem and may sell an additional 1.46 million, leaving it holding about 148,000 shares of Modem's stock.
Modem's founders, G.M. O'Connell and Robert Allen, are also selling 150,000 shares and 50,000 shares, respectively, in the same public offering.
Modem Media, founded in 1987, over time absorbed various interactive holdings of True North Communications and its agency Bozell, giving True North a 51.1% ownership stake and 83.9% voting power when Modem went public in February 1999. Interpublic became Modem's largest shareholder when it bought True North in June 2001, and in recent months has moved to sell various assets to pay down debt.