From Parliament's Standing Orders

Last night, Dr Michael Cullen walked out of Parliament to take advantage of the standing order that requires a Minister to be present.

38: Minister to be present
A Minister must be present during all sitting hours of the House. If a Minister is not present, the Speaker interrupts proceedings and the bell is rung for up to five minutes. Where no Minister appears, the Speaker adjourns the House until the time for its next sitting.

What I hope happened today is that an MP lodge a complaint with the Speaker under the following Standing Order:

394: Contempt of House
The House may treat as comtempt any act or omission which -
(a) obstructs or impedes the House in the performance of it's instructions, or
(b) obstructs or impedes any member or officer of the House in the discharge of the member's or officer's duty, or
(c) has a tendency, directly or indirectly , to produce such a result.

Clearly Dr Michael Cullen has shown contempt of Parliament by walking out. He impeded every other Member of Parliament from enacting (or defeating the enactment) of laws - a duty of every MP.

I just hope someone has the balls to write that letter.