Prime Minister Tony Abbott has rejected accusations the government is "leaning on" the industrial umpire in an effort to cut the penalty rates of workers.

In rebuffing Labor claims he had no idea how millions of ordinary Australians made a living, Mr Abbott acknowledged penalty rates were "very, very important" to the low paid.

The government is under attack from the opposition, Greens and trade unions for its submission to a Fair Work Commission review of the award system.

It wants the commission to consider the impact a softening economic environment and labour market is having on employers.

It also asked whether extra pay for working particular times of the day was appropriate in a particular industry.

While the government did not cite the hospitality and retail sectors - traditional employers of low-paid workers who benefit from shift and weekend penalties - its requests mirrors their calls for a review of loadings.

Opposition Leader Bill Shorten accused the prime minister of being out of touch with ordinary Australians.

"(He) has no idea about how millions of people earn their pay," he said.

Mr Abbott disagreed: "If you're a low-paid worker one of the things you often love to do is work late nights, weekends, because it does substantially increase your income."

As well, he wanted Australian workers to be the best paid and most productive in the world.

Labor's workplace relations spokesman Brendan O'Connor lampooned Mr Abbott's pre-election vow not to revisit the Howard government's Work Choices regime, when he famously said it was dead, buried and cremated.

"Well clearly it was only sedated until this government was elected."

Mr Abbott rejected any suggestion his government intended changing workplace rules, saying it was up the commission to set minimum pay rates.

"We think these matters should all quite properly be determined by the independent umpire and that is as it should be," he said.

Trade unions fear the award system will be undermined if penalty rates are taken away.

"Whatever this government says, we still do value our weekends in Australia," ACTU president Ged Kearney said.

The Greens believe the government is trying to wind back the pay and conditions of workers.

The commission's full bench began hearings on Wednesday.