The Fair Work Commission on Monday will begin a three-day hearing about the use of sleepover shifts.
Sleepover shifts are common in some care industries, where employees are asleep for periods overnight while on site, but are required to be on hand at a moment's notice if there are disturbances or emergencies.
The commission will hear a proposal by the Australian Industry Group which wants the sleepover shifts to be classified as a break between shifts.
The proposal has prompted multiple unions to team up to fight the application, saying employees could be rostered on for as long as 28 hours in a row before any overtime pay kicked in.
Australian Services Union NSW and ACT secretary Angus McFarland said the move was irresponsible and unfair.
"Sleepover shifts are essential to support the members of our community who may need assistance anytime during the night including people with disabilities, victims of domestic violence, and children in out-of-home care," he said.
"Sleepover shifts aren't breaks. Workers are away from their families, confined to their workplace, and struggle to get a restful night's sleep.
"They cannot leave freely and are frequently woken up at all hours to support clients in need.
"Doubling a worker's hours without decent remuneration and a real restful break is not only deeply unfair, it's negligent."
Mr McFarland said the move would jeopardise the safety of clients.
In its submission to the Fair Work Commission, AI Group said work awards surrounding the use of sleepover shifts were "ambiguous".
The group said it was unclear whether work arrangements before and after a sleepover period were considered as one continuous shift.
"Employers in this sector are between a rock and a hard place," AI Group chief executive Innes Willox told AAP.
"As unions will undoubtedly accept, they need to provide clients with consistent care before and after they sleep by engaging the same staff member to work both periods."
Assertions the group's proposal would result in longer hours for workers or staff operating while fatigued were "simply inaccurate", Mr Willox said.
"Many employees want to provide care in this way and many want toundertake a working arrangement that enables them to compress their working week by undertaking this pattern of work," he said.
"However, the current award terms fail to clarify how these arrangements are paid."
Mr McFarland said the changes would exacerbate issues with the workforce in care industries.
"Workers are already feeling burnt out and fatigued, never mind when they have to work longer hours for less pay," he said.
"Big business needs to wake up and withdraw their attack on our award.
"Sleepover shifts need to be fixed, not taken backwards."