An unlikely proposal to "flatten the tax system" at this year's budget is unhelpful and shortsighted, according to Tax Justice Aotearoa.

ACT leader David Seymour's bid to scrap the lowest tax threshold and reduce the highest tax rate would unfairly advantage the wealthy and negatively impact lower income earners.

Tax Justice Aotearoa is calling on Finance Minister Nicola Willis and the National Party to reject ACT's tax proposals at this year's budget.

"These so-called "flatter" income taxes are regressive," says Tax Justice Aotearoa chair Glenn Barclay.

"Proposals such as dropping the top tax rate to 33% would advantage the rich, while placing greater burden on the rest of Aotearoa.

"A lower overall tax base would inevitably impact negatively on revenue, which then adversely impacts services and necessary public investment," says Glenn Barclay.

"It's simply not responsible to reduce overall revenue and give tax cuts to the rich at a time when public services are under pressure, climate change challenges are growing, our infrastructure is needing better investment, and inequality and poverty continue to be spiraling problems."

“Our tax system is already inequitable and doesn’t raise enough revenue to meet these growing challenges,” says Glenn Barclay.

“These regressive tax policies would only store up problems for the future at a time when our tax system needs to be more progressive."