In a strongly worded letter submitted Thursday to Competition Commissioner Neelie Kroes, the legislators said Microsoft regards the EU's regulatory actions as a "risk factor."

"This effectively means that the Commission's actions are endangering the ability of European business to compete globally," the letter said.

The letter was signed by U.K. representatives Chris Heaton-Harris, Sharon Bowles and Peter Skinner, plus Michal Kaminski of Poland.

Microsoft has cited uncertainty over the legal principles regarding product design in the European market in recent US legal filings.

"These uncertainties could ... delay release dates for Windows or other products," the Security and Exchange Commission filing read.

Microsoft has provided copies of Vista to the Commission along with technical information, said spokesman Tom Brookes. The Commission, he said, has raised concerns regarding complaints by competitors.

In March, the Commission sent a letter to Microsoft Chief Executive Officer Steve Ballmer, saying it was concerned about certain functions in Vista and how compatible the OS would be with products from other software companies.

European Commission representatives were not immediately available for comment regarding Thursday's letter.

Heaton-Harris referred questions to Microsoft, regarding why the company thought the EU might cause a delay Vista's shipping date. "That climate of uncertainty caused through competition policy and actions already taken ... are meaning that Europe is being deprived," Bowles said.

Microsoft and the Commission have locked horns over how the company is complying with the March 2004 antitrust decision. The Commission fined Microsoft €280.5 million ($357m) in July for failing to provide technical documentation for certain protocols used by its server products.

The Commission required disclosure of the protocols to allow competitors to develop compatible products. Microsoft is appealing.

Microsoft is also appealing the entire March 2004 decision, in which it was fined €497m ($613m), before the European Court of First Instance in Luxembourg.