It was back in April last year when the US Department of Justice filed charges with Apple and several book publishers, such as Penguin and Simon & Schuster...
Source: http://www.phonearena.com/news/Apple-may-have-to-pony-up-about-500-million-in-settlements-in-a-price-fixing-case_id45755
Source: http://www.phonearena.com/news/Apple-may-have-to-pony-up-about-500-million-in-settlements-in-a-price-fixing-case_id45755