Activision's filing seeks to show the firing was justified and claims the men met with a key gaming rival, which it says was one of several violations of their employment contract.
Infinity Ward is the studio behind last fall's record-breaking release, "Call of Duty: Modern Warfare 2," and other games. "Modern Warfare 2" was No. 1 last year and has become one of the best-selling video games of all time.
The breach of contract suit claims West and Zampella held up development on other "Call of Duty" games to try to gain more money. The company is seeking to withhold additional payments to the men, who they claim also kept bonuses from Infinity Ward employees.
The men "morphed from valued, responsible executives into insubordinate and self-serving schemers who attempted to hijack Activision's assets for their own personal gain and whose actions threatened both the future of the Call of Duty franchise and future of Activision's (Infinity Ward) studio," the complaint states.
West and Zampella's attorney, Robert M. Schwartz, called the countersuit's claims "false and outrageous."
"None of the false claims of insubordination or breach of duties had any negative affect on Activision -- none," Schwartz said in a statement. "Modern Warfare 2 has been the world's most successful video game."
The lawsuit alleges the bonuses were withheld in an attempt to try to leverage other key employees to leave Santa Monica-based Activision.
Schwartz denied that claim, calling Activision's suit a tactic to withhold bonuses from other Infinity Ward employees.
The filing does not state by name which rival West and Zampella are accused of meeting with, but states they were flown by the rival to Northern California. Gaming giant Electronic Arts, which is Activision's main rival and produces the competitor franchise "Medal of Honor," is based in Northern California.
The cases are filed in Santa Monica, where Activision is based. The company is majority owned by French conglomerate Vivendi SA.