National leader Simon Bridges has been booted out of Parliament's debating chamber for disputing whether he'd made a "barnyard noise".
House Speaker Trevor Mallard chastised the opposition leader for loudly sighing earlier in the session, describing it as a "barnyard noise of the sort that would not be accepted in a junior classroom".
Mr Bridges said the Speaker was being unprofessional and making him out to be a naughty boy.
"I made no such noise, and it's entirely wrong and unfair for you as a Speaker to say that sort of unprofessional comment."
Mr Mallard then ordered him to leave the chamber.
Speaking to reporters outside the House, Mr Bridges said the Speaker had different standards for different MPs.
"When Winston [Peters] does ridiculous things ... that's charming, that's fine, that's jovial. When on our side, actually frankly nothing bad even happens, there's a very different heavy response."
Mr Bridges said he stood by his statement that the Speaker was being "unprofessional".
"I go in to do a serious job - which is to hold the government and prime minister to account - and sometimes the Speaker gets in the middle of that.
"From time to time, the Speaker does need to be reminded that it's Parliament's House, that it's for all members of Parliament, and the opposition has an important role to play."
Labour MP and leader of the House Chris Hipkins rejected that Mr Mallard was more lenient on government MPs.
"The Speaker generally tends to upset both sides of the House in relatively equal measure and that's probably a sign that he's playing down the middle."
Under Parliament's rules, MPs are not allowed to directly criticise or challenge the Speaker.
Mr Bridges and Shadow Leader of the House Gerry Brownlee were thrown out of the House late last year, prompting many of the National MPs to walk out in protest.