Regulators in Europe are reportedly set to file an antitrust lawsuit against Microsoft (MSFT) related to the company’s failure to comply with a three-year-old ruling ordering it to offer users a choice of Web browsers on Windows PCs. An investigation into Microsoft’s breach of the order was opened this past July, and the company had previously acknowledged the violation last year. “The next step is to open a formal proceeding into the company’s breach of an agreement. We are working on this,” EU Competition Commissioner Joaquin Almunia said on Thursday. “It should not be a long investigation because the company itself explicitly recognized its breach of the agreement.” Reuters reports that if the Redmond, Washington-based company is found guilty, it could face a fine of up to 10% of its global turnover. According to the report, Microsoft has already been fined more than $1.3 billion by European regulators over the past 10 years.