Labour is considering its range of options in the wake of allegations and claims made this week in Nicky Hager's new book, Dirty Politics, says party leader David Cunliffe.
Among other things, the book - published on Wednesday - implicates staff within the National Party over the release of potentially damaging information on the Government's opponents.
It claims a member of the staff of Prime Minister John Key accessed Labour Party computers and passed information on to Whaleoil blogger Cameron Slater.
In Wanganui last night Mr Cunliffe said what he had read of the book so far had left him "deeply concerned".
"And the more I read, the sadder I feel that New Zealand politics has come to this.