BRUSSELS (Reuters) - EU antitrust regulators launched an investigation on Tuesday into news and financial data publisher Thomson Reuters' use of its real-time market datafeed, saying it might block users moving to rival firms. The European Commission, which polices competition in the 27-country European Union, said the investigation was launched on its own initiative and that it did not imply it had proof of an infringement.

The Commission said it would examine whether Thomson Reuters could prevent clients from mapping Reuters Instrument Codes (RICs) to alternative identification codes of other datafeed suppliers.

"Without the possibility of such mapping, customers may potentially be 'locked'-in to working with Thomson Reuters because replacing RICs by reconfiguring or by rewriting their software applications can be a long and costly procedure," it said in a statement.

RICs -- short, numerical codes that identify securities and their trading locations -- are used to retrieve information from Thomson Reuters' real-time datafeeds which are virtual pipelines of electronically distributed real-time market data that feeds software applications developed by banks and financial institutions.

Thomson Reuters confirmed it had received a questionnaire from the Commission on the use of RICs and that it was cooperating with the Commission.

"Thomson Reuters provides its customers with consistent, dependable and convenient access to several million financial instruments from almost every electronic trading venue around the world and a vast number of other sources of valuable high quality content," the company said in a statement.

"Thomson Reuters data is reliably and consistently identified by a managed code, which we create and maintain to enable navigation of the company's global content. Our customers are at the heart of our business and we continue to work with them to explore how best to add value to our data services."

The statement added: "Thomson Reuters will fully cooperate with the EC Commission's investigation which is at a preliminary stage."

The company was formed last year by the merger of Thomson Corp and Reuters Group Plc. Its markets division competes with Bloomberg LP and News Corp's Dow Jones Newswires.

There is no strict deadline for the Commission to complete its investigation.

(Reporting by Foo Yun Chee, editing by Timothy Heritage)