Slack Technologies Inc. /zigman2/quotes/212180539/composite WORK +2.32% said Wednesday that it has filed a competition complaint against Microsoft Corp. /zigman2/quotes/207732364/composite MSFT -0.50% , alleging illegal and anti-competitive practice of abusing its market dominance, before the European Commission. "Microsoft has illegally tied its Teams product into its market-dominant Office productivity suite, force installing it for millions, blocking its removal, and hiding the true cost to enterprise customers," Slack said in a statement. "We're confident that we win on the merits of our product, but we can't ignore illegal behavior that deprives customers of access to the tools and solutions they want," said Jonathan Price, vice president of communications and policy at Slack. The EC will review Slack's complaint and then decide whether to open a formal investigation. Slack's stock has rallied 45.1% year to date through Tuesday, while Microsoft shares have climbed 32.4% and the Dow Jones Industrial Average /zigman2/quotes/210598065/realtime DJIA -2.97% has slipped 6.0%.