Labour leader David Shearer said National had not engaged with his party on the issue and had failed to treat Parliament as "the people's house."
He said John Key had falsely claimed that National had been in contact with Labour regarding its choice of Speaker.
Mr Shearer did not meet National MP David Carter, who is tipped to be the new Speaker, until yesterday.
"That was the first approach we had by Government about the appointment of the Speaker," he said.
As a result, Labour would put forward its own candidate at the election at 2pm today.
Mr Shearer said all Opposition parties backed the choice of Mr Mallard as a Speaker.
"Trevor Mallard is a passionate observer and participant in Parliament. He knows standing orders back to front and he is keen on having that job."
He said the nomination was not a stunt, and Mr Mallard "really wants the job".
"He's a very serious candidate, perhaps the most experienced person in Parliament at the moment."
- Isaac Davison of the NZ Herald
