Treasurer Scott Morrison has described Labor's $17 billion plan to close family trust tax loopholes as a "direct assault" on small business and has challenged Opposition Leader Bill Shorten to release the full details of his policy.

Describing Mr Shorten as a "till raider", Mr Morrison said the Labor plan was yet another negative policy "dripping with envy and higher taxes" that would do nothing to get Australians into jobs.

"This is another direct assault on small businesses by Labor. Bill Shorten is whacking small business families with a double tax," Mr Morrison told Fairfax Media. "He is using small businesses as an ATM, putting his hand in their till. If your family runs a small business and you have a family trust, Bill Shorten thinks you're the problem, that you're dodgy."

Mr Shorten confirmed the crackdown on Sunday, telling Labor's NSW conference he will introduce an across-the-board minimum 30 per cent tax rate on discretionary trust distributions to people over the age of 18 if he wins power.