The charges follow a complaint filled by Norwegian browser developer Opera Software in late 2007. Google, Mozilla and the European Committee for Interoperable Systems (ECIS) have all since backed the EC in the case.
After Microsoft asked the EC for more time last month, the deadline was pushed back to April 21. However the software company has once again asked for the deadline to be extended and the EC has given Microsoft until April 28 to respond to the charges.
"Microsoft confirms that the new deadline for the company to respond to the Commission's statement of objections is 28 April," said the software giant.
The EC has yet to reveal what action it plans to take against Microsoft if the company's response is unsatisfactory. It is thought Microsoft could be fined, forced to let users choose alternate browsers to install in Windows or ordered to allow users to disable IE if a different browser is desired.