National MP Nick Smith has slammed officials who drafted the government's controversial Waka Jumping Bill.

Photo: Rebekah Parsons-King

He has called them "buffoons" and "a disgrace" as Parliament continues to debate the legislation under extended hours today.

The bill was borne from the coalition agreement between Labour and New Zealand First, and would prevent an MP who leaves or is expelled from their party from remaining in parliament as an independent or in another party.

National's vehemently opposed, saying it would tear apart the democratic fabric of New Zealand society.

Dr Smith pointed to Ministry of Justice officials watching the debate this morning, before voicing his disgust at them.

"Absolutely disgusted at their attitude of just whatever the minister wants, whatever Winston Peters wants. The buffoons in the Ministry of Justice would just sign off on it."

Justice Minister Andrew Little called the remarks appalling. He said as minister he would defend public servants to the hilt for doing their job of giving advice to politicians.

"There is no question that Dr Nick Smith's conduct in relation to calling out public servants is an absolute and utter disgrace," he told the House.

The Ministry of Justice said it would not comment on the proceedings of Parliament.

"Proceedings of the House and select committees are subject to parliamentary privilege, and the Ministry of Justice will not be commenting," a spokesperson said in a short statement.

The government intends to have the law passed through Parliament this week.