Digital distributors Direct2Drive, Impulse and Gamersgate have decided not to sell Modern Warfare 2, as the game requires installation of Valve's Steamworks tools.
"We don't believe games should force the user to install a Trojan Horse," D2D told Kotaku.
Steamworks was announced for Modern Warfare 2 just weeks ago. Infinity Ward's mammoth shooter is Valve's most glamorous supporter yet. The tools fulfil an array of functions: game authentication, auto-patches, updates, achivements, anti-cheating and persistent player saves via the Steam Cloud.
But D2D - unhappy with the forced installation of software from its rival - will continue to boycott Steamworks games until Valve "decouples its retail marketplace" from the tools.