Senator Al Franken wrote this letter to the US Attorney General and the Chair of the Federal Trade Commission, saying, in part:

I am writing to encourage you to examine Apple’s content dealings with app developers to determine whether the company is engaging in anticompetitive behavior in the music streaming market. As the digital music industry continues to evolve, we must ensure that this relatively new market allows for meaningful competition and that consumers have access to important information about the products and services available to them. While I am encouraged to see increased competition in this market, I am concerned about certain business practices that have the potential to limit choices and raise prices for consumers.

And:

Apple’s licensing agreements have prevented companies from using their apps to inform users that lower prices are available through their own websites, to advertise the availability of promotional discounts, or to complete a transaction directly with a consumer within their app. These types of restrictions seem to offer no competitive benefit and may actually undermine the competitive process, to the detriment of consumers, who may end up paying substantially more than the current market price point.

I think this one has legs.