Labour's Ruth Dyson is in trouble for describing Speaker David Carter as lazy and sexist.
She's the third Labour MP to be accused of breaking the rules that protect the Speaker from allegations of bias.
Deputy Speaker Chester Borrows today told Parliament National's whip Tim Macindoe had laid a complaint against Ms Dyson, the MP for Port Hills.
"On Twitter, comments from an account in Ms Dyson's name say the Speaker is incompetent, biased, doesn't like his job, lazy, sexist, doesn't give a toss," he said.
Mr Borrows has referred the complaint to the cross-party privileges committee, which is Parliament's court and decides whether rules have been broken.
It has the power to sanction MPs if they're found to be in contempt of Parliament.
Mr Borrows said Ms Dyson had indicated to him that she didn't consider the comments to be serious.
The privileges committee is already investigating comments about Mr Carter by Labour leader Andrew Little and MP Chris Hipkins.
The case against them is over comments they made in October after Mr Carter ruled that a healthy homes member's bill in Mr Little's name wouldn't come up for its first reading until next year because it was similar to one which had already been defeated.
Mr Little told media the ruling raised "serious questions about political interference" and Mr Hipkins said it amounted to "massive political interference" in the parliamentary process.