Parliament's privileges committee is going to decide whether Labour leader Andrew Little and MP Chris Hipkins have broken the rules that protect the Speaker from allegations of bias.
If they're found guilty of contempt of Parliament they could be censured by the committee, which has the powers of a court.
The case against them is over comments they made last month after Speaker David 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.
Deputy Speaker Chester Borrows today told Parliament Mr Little subsequently told media Mr Carter's decision "raises serious questions about political interference".
Mr Hipkins had said it amounted to "massive political interference" in the parliamentary process.
"In my view, allegations that the Speaker acts on the instructions of the Government and interferes in the process for political reasons are serious matters that suggest the Speaker is biased and open to political manipulation," Mr Borrows said.
He's referred the matter to the cross-party privileges committee, which will hear evidence and make a decision.