Jami-Lee Ross has poured more fuel on the fire in his ongoing feud with Simon Bridges.
After the National leader called the Government's mental health inquiry response plans a "shameful farce", the Botany MP lashed out with a brutal takedown.
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"Are you sure you're the right person to be criticising others on the topic of mental health?" he tweeted.
A Government-commissioned report released in December painted a sobering image of mental health in New Zealand, with the Mental Health Act described as "outdated and inadequate".
The inquiry has found that the annual cost of serious mental illness, including addiction, is an estimated $12 billion. The estimated reduction in life expectancy of people with severe mental health or addiction challenges is 25 years.
The Government plans to repeal and replace the Act so that it "reflects a human rights approach, promotes supported decision-making, aligns with the recovery and wellbeing model of mental health, and provides measures to minimise compulsory or coercive treatment".
But RNZ reports the working group formed to help the response to the inquiry has been shut down by the Government and will be replaced by more working groups, much to Mr Bridge's displeasure.
Mr Ross has publically dealt with his own mental health issues, including being sectioned to a mental health facility at Middlemore Hospital in October after falling out with Mr Bridges.
Mr Bridges has previously promised to "scrupulously ignore" Mr Ross, saying he is "no longer my problem".
But it appears Mr Ross isn't so keen on returning the favour.