ACT leader Don Brash has released an open letter to the Prime Minister criticising the National Government's performance.
Dr Brash accuses John Key of running the country for the benefit of Labour and Green voters who switched to National at the last election.
A Radio New Zealand political reporter says the letter is ostensibly to tell Mr Key why Dr Brash resigned his National Party membership and sought to lead the ACT party.
Dr Brash, a former National Party leader, successfully challenged Epsom MP Rodney Hide for ACT's leadership at the end of April.
As a party leader outside Parliament, he needs to find ways to get coverage of his views, and in the letter he takes aim at policies such as Working for Families, KiwiSaver, student loans and bridging the wage gap with Australia.
He outlines past criticisms of Mr Key, including a claim that National has given up on closing the wage gap and the Prime Minister's refusal to raise the age of eligibility for superannuation - which Dr Brash says is irresponsible.
Dr Brash also accuses Mr Key of squandering the opportunity that his high popularity gives him to implement more responsible economic management. However, he says he still sees National as ACT's only viable partner.
The Prime Minister on Friday dismissed the criticisms as political posturing.
Mr Key says the Budget on Thursday will show that the accounts are doing well, and debt and unemployment levels are not as bad as they were previously predicted to be.
