Workers from the hospitality, retail, fast food and pharmaceutical industries responded with outrage, as for many Sunday staffers the decision meant a pay cut.
Later, he said: "Why should an employer think about giving workers pay rises when the Fair Work Commission can be allowed just to reduce people's pay and conditions?"
"With a significant proportion of retail and hospitality workers under the age of 24, this latest decision to cut penalty rates is another example of how young Australians are being disproportionately affected by challenges in the workforce and the growing risk they face in an increasingly flexible workforce".
The loss of this additional pay will have large ramifications for the retail industry, where one in four young Australians are now employed.
He said penalty rates were fair compensation for those workers who sacrificed their Sundays when other people were enjoying time with their families.
"Unless there is severe intervention, we are on the way to seeing a whole class of working poor in this country", Kearney said.
And pharmacy full-time and part-time workers working from 7am to 9pm will see penalties cut from 200 per cent to 150 per cent.
"They're saying the decision will increase opening hours on a Sunday but an increase in hours overall would rely on spending overall".
While co-owners of Square Sandwiches in Sydney's Australia Square, Naji Kazzi, 32, and Keith Lewis, 44, will benefit from the penalty rate cut ruling, they did not support the decision.
North Korea vows to reject Kim Jong-nam post-mortem
The men arrived in Malaysia separately between January 31 and February 7, and all left on Feb.13, the day of the murder. Kim Jong Nam, who was 45 or 46, was estranged from his North Korean relatives and had been living overseas for years.
Online, many were quick to criticise the decision and detail exactly how important penalty rates are to people on low incomes.
"Many Australians work seven days a week and we live in a 24/7 economy - this reflects consumer demand as it stands now".
Staff at Woolworths and Wesfarmers-owned businesses, including Coles, Kmart, Target, and Bunnings, are employed under wage agreements that expired long before this week's Fair Work Commission ruling on weekend pay.
Meanwhile, following the widespread backlash from workers who will suffer a pay cut, some businesses such as Lush have reassured their Sunday employees that they would continue to offer the current award.
The recent penalty rates decision was made in relation to various awards in the hospitality and retail sectors, particularly the Fast Food Industry, General Retail Industry, Hospitality Industry (General), Pharmacy Industry, Registered and Licensed Clubs, and Restaurant Industry Awards.
Guardian Australia understands the Greens will prepare a bill for release on Friday or Monday and are confident if legislation were passed before orders begin to take effect from 1 July the cuts could in effect be prevented.
"I personally disagree with the decision, when you open a business you take into consideration that holiday and weekend rates will apply and you account for that".
Up to 700,000 workers, including some of the lowest paid who need the penalty loading to survive, are affected.
"This is a bad day for workers ... rules must be changed".
For those who work the minimum three hours on a Sunday, they will now have to work an additional hour.