Details of the suit, revealed in the Wall Street Journal, show that Agency.com is seeking financial redress for iCrossing stealing staff and clients as well as "disloyalty and breach of fiduciary duty, misappropriation of Agency.com's confidential trade secrets and other wrongs".
Named in the suit are 10 individuals including Donald Scales and Marlin Jackson, who were CEO and business development vice-president at Agency.com respectively, before moving to iCrossing.
Scales is accused of breaching the conditions of his six month-long period of gardening leave, with Agency.com accusing him of taking its money but not remaining loyal during the notice period.
Jackson is accused of neglecting his duties to develop and retain customers when he was working with Agency.com to the extent of discussing iCrossing products with one of Agency.com's clients and securing the Marriott/RitzCarlton account for iCrossing before he left.
Agency.com, part of Omnicom, is blaming iCrossing's actions for the closure of its Dallas office in November last year and a "decimated Chicago office", and has filed the suit in Dallas.
It says that iCrossing's actions have cost it $19.5m and is seeking damages in the suit.