Massachusetts, the only state government still pursuing antitrust claims against Microsoft through the federal courts, made its allegations in a legal filing with US District Judge Colleen Kollar-Kotelly in Washington, D.C.
"If Microsoft is taking steps to hobble the competitive effectiveness of these rival products and thereby supplant them, such serial killing of competing technologies is a serious and troubling prospect," read the three-page filing, which offered no details.
In addition, Massachusetts charged Microsoft with demonstrating "troubling business behaviour" that could run afoul of existing court orders.
This move comes as the battle for Web search dominance is heating up, with Yahoo saying on Wednesday that it will drop Google's technology in favour of its own. At the same time, Microsoft is trying to find ways to make more money from Web searches by integrating such features more closely into its Windows operating system.
"Given the vague and unsubstantiated nature of the allegations, it's difficult to respond," Microsoft spokeswoman Stacy Drake said on Friday. "However, we are always willing to sit down and discuss any issues of concern. We are firmly committed to firm compliance with the consent decree and all matters in antitrust law."
In 2002, Microsoft entered a consent decree with the Bush administration, which Kollar-Kotelly accepted, to settle the antitrust case. It also established a schedule for ongoing antitrust oversight of the company's actions.
On Thursday, Microsoft said it will voluntarily alter a music-purchasing feature in Windows XP in response to criticism from the US Department of Justice. A joint filing from Microsoft and the Justice Department is expected to be submitted to Kollar-Kotelly later on Friday.
Massachusetts Attorney General Tom Reilly has objected to the 2002 peace accord in the antitrust dispute and has kept fighting.
In November, a federal appeals court in Washington, D.C., heard the state's arguments in favour of overturning the settlement but has not yet ruled. A decision is expected at any time.
