Labour MP Louisa Wall was given a speaking slot in Parliament by the National Party to talk about suicide after her own party denied it to her.
In an impassioned speech to the House on Thursday National MP Matt Doocey said it was "absolutely disgusting" that Labour would "block" Wall from speaking.
Wall is part of a cross-party mental health group that recently published a report on suicide, set to be debated in the House on Thursday.
But Wall was not given a slot to speak by her Party, something she admitted to Stuff was frustrating and "unexpected".
"Labour did not prioritise me on the speaking list. National’s Dr [Shane] Reti offered me his slot – I was very grateful to accept this invitation," she said.
She used the opening of her speech to thank Dr Reti for allowing her to take part in the korero.
In his speech to the House on Thursday Doocey said as a founding member of the cross-party group, Wall should be allowed to speak.
"She championed this report and worked hard on it. She has been blocked from taking a call on this debate so National has given her one of ours because it is important she has a call."
Labour MP Kieran McAnulty told Stuff the Party had prioritised its ministers with responsibility in the area of mental health.
"As the Government, we decided it was important we allocate our slots to the most relevant ministers, including the health and youth ministers who are doing work in this area."
It's the second time Wall has broken ranks with Labour in a week. Earlier this week she made headlines for accusing China of forced organ harvesting from Uyghur and Falun Gong political prisoners.
"The Uyghur population, and also the Falun Gong population, both have been designated as prisoners of conscience," she said. "We know that they are slaves. We also know that they're being used to harvest organs."