He is also suing former ministers Paula Bennett and Anne Tolley but that is no surprise. They have always been targets.
The really stunning aspect of the new action is its timing so close to the date he is due to become Acting Prime Minister for six weeks.
Even if he had a water-tight case – and there is no evidence that he has - wouldn't he delay it for the sake of a peaceful transition?
The untidiness in handing over to Peters stretches to the Three Strikes debacle as well.
To be fair to Peters, most of the blame lies with Justice Minister Andrew Little who has had to cancel a planned Cabinet paper at the behest of Peters.
Little has been talking for months about getting rid of the Three Strikes law, without getting sign-off from coalition partners New Zealand First or the Cabinet.
Little was led to believe from Peters that he opposed it.
When Little was asked about New Zealand First support for Three Strikes repeal 10 days ago, he said: "Winston has an interesting point that he puts to me. He says he is sick and tired of innocent New Zealanders getting mugged on the street and then getting mugged as taxpayers a second time."
But even so, a nod and wink from Peters is not a commitment.
Ardern and Little have tried to spin this hiccup as just a part of the healthy disagreements within coalition, which it is not.
It is a failure of proper process in coalition management.
There have been many instances when Labour ministers have said they will be doing something because it was in the party manifesto.
They have not caught up with the fact that the Labour manifesto has no standing as a document of promises any longer without agreement from NZ First and the Greens.
The Speech from the Throne, the Coalition Agreement and the Confidence and Supply Agreement are the only ones that count.
Ardern should have made that clearer to ministers. Peters takes over from Ardern tomorrow in terms of answering questions in the House and thanks to him they will come armed and loaded.
National will be praying it is a sign of things to come.