IGN-owned digital games firm Direct2Drive is refusing to sell Modern Warfare 2 on PC because of its integration with Valve's Steamworks.
All PC copies of Modern Warfare 2 will come with Steamworks, not just the ones sold on Steam, and will benefit from Steamwork's variety of features, including community integration, updating, DRM and stat tracking.
However, the Steam online store is a direct competitor to Direct2Drive and similar digital services.
And Kotaku is reporting that other digital distributors, including Impulse and Gamersgate, have also pulled support for the title.
Direct2Drive told Kotaku:
"At Direct2Drive, we believe strongly that when you buy a game from us, you shouldn't be forced to install and run a third party software client to be able to play the game you purchased. Because COD MW 2 requires you, the consumer, to do that, we aren't able to offer the game via Direct2Drive at this time.
"We don't believe games should force the user to install a Trojan Horse."
Modern Warfare 2 is due for release on Tuesday and is being billed as the biggest entertainment launch of all time.