"Accusations that the Speaker has shown partiality in discharging his or her duties have in the past been judged very seriously, given the special position the Speaker holds."
Mr Mallard, who has ambitions to be Speaker, has frequently been ejected from Parliament.
Yesterday Mr Mallard said he did not believe any change was required to Parliament's rules. He stood by his criticism, saying he praised Speakers when they were fair but criticised if they were not. "I've indicated I think Lockwood Smith was a very good Speaker, he ruled fairly and evenly. I think Mr Carter on occasions has not been up to that standard."
Otago University constitutional law expert Andrew Geddis said if Mr Mallard had made the comments in his tweet out loud in Parliament, he would not have got away with it.
"It's pretty on the point. The general rule is that bringing the Chair into disrepute or challenging the Speaker is a contempt of the House."
Mr Geddis said social media had made the Speaker's job harder and it was possible the Speaker was looking for a way to deal with Twitter comments himself, as soon as they came to his notice, rather than having them referred to the Privileges Committee.
Sledging the Speaker on Twitter
Trevor Mallard, May 13:
2nd week in a row where the Speaker looked like a Mafia don running his @NZNationalParty protection racket."
April 9: "Facial expression is important and Speaker shouldn't be seen to cheer for the Prime Minister."
June 6, 2013, after walking out over ruling on Peter Dunne's status as party leader: "Farcical ruling" and "I agree with @PeterDunneMP 'If you lose confidence in the Speaker then frankly you start to lose confidence in the whole system'."
Chris Hipkins, May 13: "The Speaker has enough trouble keeping control of what is happening in front of him in the House, forget trying to censor Twitter!"
March 27, 2013, ejected from Parliament: "Speaker Carter clearly has double standards."