Prime Minister Malcolm Turnbull has warned Australia’s big five banks not to lie to customers if they try and pass on the $6 billion levy proposed in the federal budget.

Mr Turnbull also acknowledged an increase in the Medicare levy will be an extra tax on families, but said its role in funding the NDIS made it worthwhile.

It has been suggested the major banks may move quickly to raise mortgage rates by up to 0.15 per cent to compensate for the budget measure.

The Prime Minister said that would be unwise.

“That would be really excessive,” he told Sky News on Wednesday, noting there was already a lot of concern about the conduct of banks.

The Australian Competition and Consumer Commission (ACCC) would be watching the banks “very, very carefully indeed”, he said.

Treasurer Scott Morrison told the Seven Network the ACCC would be “keeping an eye on them to make sure they don’t lie to their customers about this”.

The $1.5 billion the levy raises each year would come out of corporate profits of $30 billion this year, he said. “He can do their bit for budget repair.”

Mr Turnbull said it was only fair the “most profitable banks in the world” were levied to help balance the nation’s budget and similar measures were in place around the world.

Under new measures, banks with liabilities of more than $100 billion – Westpac, ANZ, Commonwealth, National Australia Bank and Macquarie Group – will be slugged 0.06 per cent on those liabilities each year from July.

Crossbench senator Jacqui Lambie predicted the banks would fight the levy all the way as she renewed her call for a royal commission into bank misconduct.

Labor said the government’s “package of half measures” was no substitute for a royal commission.

Nevertheless, it will support the levy, shadow treasurer Chris Bowen confirmed.

The Australian Bankers’ Association CEO Anna Bligh said the levy was introduced without consultation, describing it as a “political tax grab to cover a budget black hole”.

Mr Turnbull dismissed as “nonsense” her claim the levy was a threat to the stability of the banking system.

Medicare levy

Mr Turnbull the Medicare levy hike would offer comfort to the families of children with disabilities.

“Are you going to turn around and say in a few years’ time to parents of disabled kids, ‘sorry, there’s no money in the till’?” he said on ABC radio.

“Now it is fully funded so you’ll know if you have a disabled child … you will know the money is there, and it’s there because Scott Morrison included it in the budget last night.”

Mr Turnbull said the Senate had not backed the government’s savings measures to allow it to fund the NDIS by other means.

The government examined the half per cent allowance already in the Medicare levy to help fund the NDIS and decided to add another half point – lifting the levy to 2.5 per cent total from July 2019.

“For many Australian families, they will feel it … but there’s a benefit,” Mr Turnbull told Sky News.

“This is just, fair, responsible.”

Crossbench senator Nick Xenophon said his team would look at the measure “favourably”.

“We want the NDIS to be successful and to work and to deliver the enormous potential it can for the people with disabilities,” he told ABC TV.

Labor has not ruled out supporting the increase, although Opposition Leader Bill Shorten said he was not convinced it was the only way for the government to fund the NDIS.

“We’re not sure the case is made just to automatically increase the taxes for everyday Australians,” he told Channel Seven on Wednesday.

“If the government is looking for some extra money, they don’t need to give a tax cut to millionaires on July 1 and they don’t need to go ahead with corporate tax cuts.”

Shadow treasurer Chris Bowen said the opposition would take time to respond to the proposed increase.

“It would be irresponsible to rule out supporting it,” he told ABC radio.

– With AAP