Ten members of the US House International Relations Committee are questioning the European Commission's decision to fine Microsoft £331m for anticompetitive practices, saying the US has addressed Microsoft antitrust issues sufficiently.
The lawmakers, five Democrats and five Republicans, sent the open letter to EU competition commissioner Mario Monti, which suggested that the fine was unnecessary after the US Department of Justice's antitrust lawsuit and settlement with Microsoft.
The DOJ's actions "addressed and resolved the same matters" as the EU investigation, the letter said.
"The [US] court's final judgment established a comprehensive regulatory scheme that not only resolved past conduct, but also created a detailed compliance structure to address future competitive concerns that might arise," the letter said.
"Because this exact issue was raised and resolved during the US settlement, it should not have been an area of concern for the EU"
The letter noted that the US and EU signed a 1991 antitrust co-operation agreement, and the European Commission's fine was "difficult to understand" with the agreement in place.
The antitrust agreement, strengthened in 1998, seeks to avoid conflict between the US and EU on antitrust issues "where one nation clearly has jurisdiction", the letter said.
"We should also note that this case involves a US company, that the complaining parties in the EU were primarily US companies and that all of the relevant design decisions occurred in the United States."
The European Commission also ordered Microsoft to offer a version of its Windows operating system without the Windows Media Player software within 90 days.
The fine will discourage US companies from marketing their products in Europe, lawmakers said.
"This effort by the commission to address issues that were previously settled in the US courts will undermine the global competitiveness of many US firms, impede American job growth, and impair innovation in many US sectors," said representative Robert Wexler.
A spokeswoman for Wexler, whose office drafted the letter, said the lawmakers hope the letter will prompt the commission to reconsider its fine.
The commission's decision to write its own rules could force software companies to write Windows-based software to the EU's restrictive standard, "essentially dictating US customer experience", or to write two different versions for each piece of software, one for the US and one for the EU, Wexler's spokeswoman said.
"The issue is not the merits of the DOJ settlement," she added. "It is the precedent set by potentially conflicting regulations."
Two different versions of Windows operating systems would hurt small developers that are writing Windows-based programs, said the spokeswoman, claiming that Wexler had already heard from developers who would be affected.
"While Microsoft has the money and resources to handle two versions, the small developers, who write the majority of programs people actually use in their day-to-day experience, do not have those kind of resources.
"Establishing two versions of an operating system means that all of these small US developers now can't sell their products in the EU without significant and costly revisions," she said.
Grant Gross writes for IDG News Service