Sunday penalty rates will be cut for hospitality, retail, pharmacy and fast food employees, the Fair Work Commission says.
Hospitality and retail employees will also see their public holiday rates cut from 250 per cent to 225 per cent.
The FWC said it agreed with the Productivity Commission there were likely to be some "positive" employment effects from the reductions.
"The evidence also supports the proposition that a reduction in penalty rates is likely to lead to increased trading hours, an increase in the level and range of services offered on Sundays and public holidays and an increase in overall hours worked," FWC president Iain Ross said on Thursday.
However, Mr Ross noted Sunday penalty rates would still be higher than for Saturdays.
"Generally speaking, for many workers, Sunday work has a higher level of disutility than Saturday work," he said.
"Though the extent of the disutility is much less than in times past."
Sunday rates for hospitality workers will fall from 175 per cent to 150 per cent while those for fast food workers will drop from 150 per cent to 125 per cent.
Retail workers face a reduction from 200 per cent to 150 per cent.
Pharmacy workers who work from 7am to 9pm will see their penalties cut from 200 per cent to 150 per cent.
Mr Ross said the changes would provide greater consistency to penalty rate settings in the hospitality and retail awards.
Australian Council of Trade Union president Ged Kearney said workers on minimum wages relied on weekend penalty rates to survive.
"This is a bad day for workers in this country," she told reporters.
Australian Retailers Association executive director Russell Zimmerman said the decision would grow the sector.
"Reducing these rates from double time to time and a half, will increase retail growth nationally and reduce the unemployment rate in Australia," he said in a statement.
Ms Kearney said that was a "complete furphy".
"People whose pay is going to be cut ... will simply have to work more hours to make up that take-home pay."
The ACTU estimates the FWC decision will cost low paid workers up to $6000 a year.