Opera, backed by an industry coalition, said it has complained that Microsoft illegally ties its Web browser, Internet Explorer, to its dominant Windows operating system.
Microsoft is also "hindering interoperability by not following accepted Web standards," the company said.
Both make it difficult for Opera to compete, it said.
The complaint is the first against Microsoft since a European Committee for Interoperable Systems (ECIS), a long-time opponent of Microsoft. ECIS issued a statement critical of the software giant.upheld a . Opera is a member of the
"By tying its Internet Explorer product to its monopoly Windows operating system and refusing to faithfully implement industry accepted open standards, Microsoft deprives consumers of a real choice in Internet browsers," ECIS lawyer Thomas Vinje said in the statement.
Opera's complaint echoes a U.S. case from 1998, in which the U.S. Justice Department won a major judgment against Microsoft for competing illegally against another browser, Netscape.
Opera asked the Commission to force Microsoft to unbundle Internet Explorer. It also asked the Commission to require Microsoft to follow "fundamental and open Web standards."