Creating paid-for games that can be played on the free Linux operating system "works against the goal of freedom", according to Richard Stallman, founder of the Free Software Foundation and the GNU OS.
He described the planned games as "unethical" because they deny freedom to their users. Games developer Valve recently started a Linux blog to publicise work on an open source version of its Steam online games service.
The team has already successfully ported the zombie first-person shooter Left 4 Dead 2 onto the Ubuntu version of Linux and is now working to make a fully-featured Steam client running on Ubuntu 12.04.
"In direct practical terms, this development can do both harm and good," said Stallman. He pointed to the fact that Windows users may try out Linux and then replace their paid-for Microsoft operating system with the free Linux system.
However, he said a more indirect effect - where Linux users start to associate the OS with paid-for software - was a huge downside.
"Any GNU/Linux distro [distribution] that comes with software to offer these games will teach users that the point is not freedom. Non-free software in GNU/Linux distros already works against the goal of freedom. Adding these games to a distro would augment that effect."
The project had been gaining a lot of support in the comments section on Valve's blog. "I've been using Ubuntu for so long now and I've completely detached myself from Windows. (the only reason i stopped buying games for PC) and now I can buy again" said user Xorrito.
Tom Mcloughlin added: "Thank you Valve. Thank you for contributing to the Linux community. Thank you for allowing Linux users to game on their choice of system. Thank you for everything. Steam is amazing."