European Union Competition Commissioner Neelie Kroes has accused Microsoft of orchestrating a "co-ordinated campaign" to discredit her.
Neelie Kroes has led the fight against Microsoft
Ms Kroes' comments have come as her department and the US software giant continue to clash over Microsoft's forthcoming Vista operating system.
In an open letter to the Financial Times, Ms Kroes insisted she was not running a "vendetta" against the firm.
Microsoft said it looked forward to constructive talks with the Commission.
With Vista currently due for release early next year, Ms Kroes wants to see changes to the European edition of the operating system to better open it up to rival software providers.
Vista is due for release next year
She has expressed concern that Vista will contain too many Microsoft applications, thereby not giving rivals a proper chance to persuade consumers to choose their products as an alternative.
Microsoft has denied that there is a problem and has warned that the European Commission's actions could delay the release of Vista in Europe.
Ms Kroes said in her open letter that it was "categorically not the case" that she wanted to prevent Microsoft from improving the security of its operating system.
She also denied charges that her actions could hit Microsoft-related jobs in Europe.
"If jobs are to be created as a result of Vista's release, any such job creation would only be enhanced with the release of a version of Vista which allowed others to compete on the merits of their products," she said.
Her comments are just the latest twist in Microsoft's long running struggle with the European Commission over its business practices.
The firm was fined 497m euros ($629m; £335m) for anti-competitive behaviour in 2004, and was further hit with a 280m-euro penalty earlier this year for failing to meet demands that it share technical information with rivals.
Brussels has also threatened Microsoft with ongoing daily fines over the same issue.