The European Union has begun an investigation into whether or not Standard & Poor’s, the international credit rating company, has violated antitrust laws by overcharging its customers for the use of Cusip numbers. Cusip numbers, nine digit numbers assigned to companies’ securities in order to help track trades, are sold to companies by Standard & Poor’s.

The service is allowed to operate as a natural monopoly, as reported by the Wall Street Journal, because having more than one identification system would complicate the trading system. While accepting this fact, the EU’s investigation is looking into whether or not Standard & Poor’s is overcharging for the service.

A spokesperson for S&P told the Wall Street Journal that the company “strongly disagrees with the EC’s preliminary assessment and believes the Commission has grossly undervalued Standard & Poor’s effort, expertise and costs required to operate a global identification system that benefits millions of investors and market participants world-wide.”