A complaint filed with the US District Court in Manhattan has marked an escalation in the rivalry between the two companies. Nielsen alleges that the comScore Extended TV service will use PPM data, which violates an agreement between the two companies.

In a statement, comScore said: “We can confirm that there is a dispute regarding interpretation of the 2013 FTC consent decree, which resulted from Nielsen’s acquisition of Arbitron that provides comScore with access to certain Nielsen data. The dispute is being addressed through binding arbitration. Due to the pending nature of these legal proceedings, we have no further comment at this time.”

Nielsen bought Arbitron in 2013 and the Federal Trade Commission allowed the acquisition when Nielsen agreed to license PPM data to comScore, to preserve competition for “cross-platform” measurement service.

Nielsen said in 2014 it contracted to let comScore use PPM data to measure both TV and online audiences. But alleges that comScore’s new Extended TV service violates that agreement because the contract didn’t allow the data to be used for individual, stand-alone services.

However, in a letter attached to the complaint, a comScore lawyer said Extended TV qualifies as a “cross-platform” service, and is “not limited to linear TV estimates as it measures content across multiple platforms, including but not limited to television, online, mobile, tablets, etc.”

Nielsen alleges that comScore is seeking to offer Extended TV at a lower price than Nielsen’s service, thereby cutting into Nielsen’s client base.