Shorten to oppose 'radical' super change

Opposition Leader Bill Shorten is out spruiking his alternative budget, rallying against retrospective superannuation changes.

Labor will oppose the government's crackdown on super tax concessions for high income earners, which will affect existing accounts.

"None of our changes will be retrospective because I really don't like retrospective laws," Mr Shorten told Alan Jones on 2GB radio, the morning after presenting his budget reply speech.

"This is quite a radical thing, that they have said we're going to (have) retrospective changes in superannuation," he said.

"It is very undermining of the stability of the superannuation system."

He later told ABC radio when Labor embarks on changes he wants to make sure they're sensible.

"When you make a retrospective change to a tax law, you're not just hitting people with a certain amount in their super, you're undermining every Australian's confidence in the superannuation system," he said.

Mr Shorten accepted there should be a tax cut for small businesses, but only for those with a $2 million annual turnover.

He also defended the policy to impose an $8,000-a-year cap on government loans for private vocational education.