Federal Treasurer Scott Morrison says the concept of workers paying less tax if they accept penalty rate reductions would be "innovative".

Mr Morrison told the ABC the country should not be locked into "yesterday's politics" when it comes to industrial relations, following Prime Minister Malcolm Turnbull's prediction that a more flexible system was inevitable.

"What you want is a tax system and a payment system that locks together, and a labour market system that links into that to ensure that you're better off working than being on welfare," Mr Morrison said.

"We need the flexibility in our system to ensure we have this agile and innovative economy."

The Government has stressed any changes were a matter for the independent national workplace relations tribunal, the Fair Work Commission.

The commission lowered Sunday penalty rates for some workers last year.

Mr Morrison said changes to the system could help disabled workers and the long-term unemployed find jobs.

"I don't know why anyone would want to rule out anything that would help young people get into jobs," he said.

He also criticised the Opposition for its strong stance on maintaining penalty rates, labelling it obstructive.

"If the Opposition Leader Bill Shorten wants to go back to yesterday's politics and drag us into a pro or negative penalty rates debate, I don't think that helps the economy," he said.

Liberal Party out of touch, Shorten says

Mr Shorten dismissed Mr Morrison's comments over the need for an adult discussion, saying Labor had 110 years of "being mature" about the wages of workers.

Mr Shorten said there was a "world of difference" between Mr Morrison's comments and Labor's proposals, which he said were designed to lift wages of workers.

"There's no plan from the Liberal Party to lift the wages of Australian workers," he said.

"All they're saying is they want to cut Sunday penalty rates."

Mr Shorten also criticised comments made by Mr Turnbull on Tuesday.

"The idea that somehow our penalty rates are a matter of history, as Malcolm Turnbull said, just shows you how out of touch the Liberal Party is," he said.

Shadow employment minister Brendan O'Connor told the ABC that penalty rate cuts were "frightening" for many workers.

Mr O'Connor did not rule out support for the changes, but said Labor would need to see the details of any proposed tax credit arrangements.

"You'd want to see the proposal, but I would have thought if you want to start looking at tax reform, you could be looking at reducing the tax rate for small businesses, rather than trying to work out a very complicated arrangement to repay workers money for cutting conditions," he said.

"It would introduce significant red tape."

Mr Turnbull said yesterday differences in penalty rates between Saturday and Sunday were a characteristic belonging to an outdated economy.

"The only reason they're different, I assume, is history," he told radio station 3AW.

"I think over time you will see a move to a more flexible workplace."

The Productivity Commission is examining penalty rates and workplace relations at the request of the Government.

The Commission released a draft report in August.