Parliament's Speaker, Trevor Mallard, is expected to appear before a select committee on Wednesday to be questioned about a costly legal dispute.

Mallard last week publicly apologised for comments he made in which he wrongly claimed an accused rapist was working on Parliament's premises.

A staffer was stood down and then launched defamation proceedings, which were later revealed to have cost the taxpayer more than $330,000.

Both National and ACT have declared they have lost confidence in the Speaker and have called for his resignation as they believe he is no longer fit for the role.

This morning, Prime Minister Jacinda Ardern told Morning Report over the years Opposition parties had claimed no confidence in the Speaker and "unfortunately, it tips into the political from time to time".

"I have confidence in the Speaker. Clearly, he has made a mistake and he himself is open about that.

"On this particular issue, the Speaker himself, I'm advised, was aware that a select committee may choose to ask him to come and answer questions. He has proactively contacted the chair to arrange a time."

Governance and administration select committee chair and National MP, Barbara Kuriger, said Mallard rang her late yesterday to confirm he was willing to attend the meeting.

Kuriger said the Clerk of the House was in the process of organising the selection committee meeting for Wednesday.

"We need to send a letter to the Speaker from me as the chair, inviting the Speaker to attend the meeting, to which we would expect his reply given that he has already notified me that he is willing to attend.

"Then tomorrow we will have some further discussions with the clerk around the process of how the meeting will work."

She said she was not going to pre-empt anything but there were questions that National wanted answered about the cost and how it was paid.

Text by By Charlie Dreaver of RNZ