Microsoft Corp confirmed on Wednesday a report that it had received a one-week extension from EU antitrust regulators to respond to charges that it had sought to thwart rivals by bundling its web browser with Windows systems.

Microsoft confirms that the new deadline for the company to respond to the Commission's statement of objections is April 28, a spokeswoman said, referring to an unsourced reference to a new deadline reported on the website of the Financial Times.

A spokeswoman for the European Commission said she could not immediately comment.

Last month, the European Union executive pushed back the original deadline to April 21 after the giant U.S. software company asked for more time. It charged the company on January 15 with infringing EU rules by abusing its dominant position.

The bundling of its Internet Explorer to Windows shielded Microsoft from head-to-head competition with other browsers, and that also harmed product innovation and reduced customer choice, the Commission had said.

Microsoft has said the Commission may order the company and equipment makers to obligate users to choose a particular browser when buying a computer, or that multiple browsers be made available on new Windows-based computers. This could come on top of a possible hefty fine. Separately, trade group ECIS -- which numbers International Business Machines Corp, Nokia, Oracle Corp and Sun Microsystems Inc among its members -- joined in the case against Microsoft on Wednesday.

ECIS said it had been accepted as an interested third party in the Commission's case.

Smaller, more innovative, browser developers need a level playing field, ECIS spokesman Thomas Vinje said in a statement.

Google Inc, which offers the Chrome browser; the Mozilla foundation, producer of the Firefox Web browser, and privately held Norwegian company Opera have already added their voices to the case against Microsoft.

(Reporting by Foo Yun Chee; editing by David Brunnstrom and Gerald E. McCormick)

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