A spanish body representing open-source software users has filed a complaint against Microsoft Corp to the European Commission, in a new challenge to the Windows developer following a big fine earlier this month.

The 8,000 member-strong Hispalinux, which represents users of the Linux operating system, said Microsoft had made it hard for users of computers sold with its Windows 8 platform to move to Linux and other systems.

Hispalinux said Windows 8 contains an "obstruction mechanism" called UEFI Secure Boot that controls the start-up of the computer and means users must seek keys from Microsoft to boot up another operating system.

The commission fined Microsoft 561 million euros (US$729 million) on March 6 for failing to offer users a choice of web browser.