Federal Labor has pledged to crack down on wealthy Australians who use family trusts to avoid paying income tax.

Opposition Leader Bill Shorten wants to impose a 30 per cent tax rate on distributions from family trusts to make the tax system fairer.

It would target high-income earners who use trusts to split money to other family members in lower tax brackets, which cuts their tax bill.

Mr Shorten said 98 per cent of Australians would not be affected by the crackdown.

"Every year in Australia there are some fortunate high-income earners who use discretionary trusts to park their money in a lower tax bracket. And the rest of the community are left to subsidise this," he said.

"Most of this is completely legal, but that doesn't make it right, that doesn't make it fair.

"Our system should not be subsidising upwards."

The tax would apply on distributions made to people over the age of 18.

It would raise $17 billion in revenue over the next decade.

'We're not abolishing trusts'

But the Opposition said trust arrangements used by farms, charities and deceased estates would be exempt.

"We're not abolishing trusts. This is about trusts serving their true purpose, so that distributions are taxed fairly," Mr Shorten said.

"It makes our tax system fairer, it makes our budget stronger, and it's the right thing to do."

Finance Minister Mathias Cormann called the plan an attack on small business.

"This is ultimately going to be a tax hike, in particular, on the many small business operators across Australia who use trusts structures as a legitimate way of managing their financial affairs," he said.

"Bill Shorten is going to try and create this impression that he can take $17 billion out of the economy but no-one's going to have to pay.

"Small business people across Australia will want to know where he's going to get that $17 billion, out of which pockets?"