The Labour Party says police's refusal to take further action about allegations made in Nicky Hager's book Dirty Politics is deeply unsatisfactory.
Senior Labour MP David Parker wrote to police in September last year to ask them to look into allegations made in the book, which include the hacking of the party's computer system.
Police responded yesterday with a letter saying the computer breach raised privacy and ethical issues, but there was no evidence of criminal offending.
Labour general secretary Tim Barnett said that response took far too long and was a dismissive way to treat serious allegations.
He said the police closing the case was not the end of the matter for the party, which would be taking further action.