Labour MP Andrew Little has accused Justice Minister Judith Collins of bullying and intimidation and challenged her to send "thuggish guys" to serve him with defamation papers.
Ms Collins threatened to sue Mr Little, Mr Mallard and Radio New Zealand in March over an interview which linked her to the leak of a sensitive email from former National Party president Michelle Boag.
The High Court yesterday confirmed Ms Collins has launched defamation action against Mr Little and Mr Mallard - though no action has been lodged against Radio New Zealand.
Both Labour MPs remain defiant, saying the case is unlikely to make it into the courthouse.
They are refusing to cooperate with legal requests to allow court papers to be served to them.
Mr Little said the minister would need to hire process servers to track him down outside of parliament grounds and issue him with the papers.
He threatened to film the servers issuing him with the papers.
"They tend to be leather jacket wearing thuggish guys, which is fair enough because they have a tough job to do. They're not the sort of people that you'd want around your family home. It won't be a good look.
"This is about Judith Collins bullying and intimidating. She gets off thinking people will be cowed into submission. Well we won't be. If she wants to have a fight then we will go to court."
An email from Mr Little to Ms Collins' lawyer alleged the action against him was motivated by "political animus".
"I have no intention of assisting your client in this pernicious enterprise. It is my intention to cause her the utmost inconvenience and embarrassment in her prosecution of this matter."
Mr Mallard late yesterday confirmed he was also refusing to cooperate with Ms Collins' court action.
"I see no reason to co-operate in what is clearly a vexatious action."
He did not believe a full court hearing on the matter would eventuate.
"A substantive trial is exceptionally unlikely."
Mr Little said it was unlikely the case would ever go to trial as Ms Collins would not want to be questioned in a witness box.