Basically, the complaint is that S&P is the sole supplier of unique identifiers for securities in the US for the American Banking Associations, and it has been using that status to extract payments from people who want to use those identifiers:

Each security such as a stock or bond has a unique number to ensure there is no confusion when it comes to clearing and settling a trade in that security.

Standard & Poor’s operates the CUSIP service bureau on behalf of the American Bankers Association, the sole issuer of identifiers for U.S. securities.

Standard & Poor’s says it charges a license fee when the numbers are used for purposes other than clearing and settlement.

The complaints focus on whether Standard & Poor’s can charge financial market data vendors such as Thomson Reuters and Bloomberg News as well as end users of these identifiers, such as asset managers and banks.

It is alleged that S&P forces vendors to cut off financial institutions from data feeds on U.S. securities unless they have licensing agreements.

These are serial numbers, and as such, they should not be protected by IP law, and the EU is going after them on this.