Yesterday's ruling against Microsoft by the European Court of First Instance has sent a shiver through the American technology sector, as other computer giants wonder if they could be next to feel the force of Europe's tough competition policies.

Intel, Rambus and Qualcomm are already under investigation by the European Commission and other US companies fear that the Microsoft ruling will encourage smaller rivals in other sectors to take their complaints to European courts rather than the US anti-trust system.

The court's decision shows clearly that Europe is determined to take a tougher approach to monopoly issues than the US, where a long regulatory battle over similar issues left Microsoft almost unaffected.

In its 2002 settlement with Microsoft, the US justice department told the software giant to share its application programming interfaces with other companies and appoint a panel of three people who would have full access to Microsoft's systems, records and source code for five years in order to ensure compliance. Microsoft did not, however, have to change any of its code nor undertake not to bundle other software with Windows in the future.

Nine states and the District of Columbia, which had taken the action jointly with the justice department, rejected the settlement as too lenient, and some critics suggested that the settlement reflected the Bush administration's unwillingness to take tough action against America's biggest corporations.

In a statement yesterday, Thomas Barnett, assistant attorney general for the justice department's anti-trust division, criticised the European court decision. "We are . . . concerned that the standard applied to unilateral conduct by the court, rather than helping consumers, may have the unfortunate consequence of harming consumers by chilling innovation and discouraging competition. In the United States, the anti-trust laws are enforced to protect consumers by protecting competition, not competitors," he said.

Republican congressman David Reichert also condemned the European ruling, declaring that the commission, far from standing up for diversity and competition, was simply trying to hobble US companies.

"This ruling sets a dangerous precedent that says Europe is closed for business to those companies who invest the capital and resources necessary to lead a market," he said.

Mr Reichert, whose congressional district is in Washington state, where Microsoft has its headquarters, suggested that other US companies might have to price such court rulings as part of the cost of operating in Europe.

"I would urge successful companies that do business in Europe, as well as the many small partners who work with those companies, to ask themselves this key question: who will be the next Microsoft?" he said.

Mr Reichert hinted at introducing legislation in Congress to protect US companies from similar European court rulings, although it is unclear what form such legislation would take.

Wall Street shrugged off yesterday's decision, which analysts said was not a surprise, and the Software and Information Industry Association, which represents some of Microsoft's smaller rivals, welcomed the ruling.

The run-up to the ruling

December 14th, 1998: Sun Microsystems files antitrust complaint to the European Commission, alleging that Microsoft is abusing its dominant market position.

September 17th, 1999: Mario Monti sworn in as European Union competition commissioner.

August 3rd, 2000: The Commission issues charges accusing Microsoft of failing to supply Sun with essential information about the Windows operating system.

August 30th, 2001: Microsoft receives a second set of antitrust charges, this time alleging it has illegally bundled Media Player software into Windows.

August 6th, 2003: The Commission sends a third set of charges, outlining possible punishments.

March 17th, 2004: Talks between Steve Ballmer, Microsoft's chief executive, and Monti on a settlement break down.

March 24th, 2004: The Commission issues a formal decision finding Microsoft broke EU competition rules by abusing its dominant market position. It imposes record €497 million fine.

June 7th, 2004: Microsoft appeals against the ruling at the Court of First Instance.

November 22nd, 2004: Neelie Kroes replaces Mr Monti as competition commissioner.

December 22nd, 2004: The court refuses to suspend the Commission's sanctions and orders Microsoft to implement them immediately.

December 22nd, 2005: The Commission issues a fourth set of charges, accusing Microsoft of failing to comply with the March 2004 ruling. It threatens a daily fine of €2 million.

July 12th, 2006: The Commission imposes a €280.5 million fine on Microsoft for its failure to comply with the 2004 ruling.

March 1st, 2007: Microsoft receives its fifth set of formal antitrust charges.

September 17th, 2007: Court of First Instance rules on Microsoft's appeal against Commission's three-year-old antitrust decision.