Unison has applied to appeal last month’s Court of Appeal ruling that overturned a back-pay liability of more than £400m owed by care providers to sleep-in care workers.
The trade union confirmed that it had taken the first step in instigating appeal proceedings in applying to have leave for the appeal to be heard in the Supreme Court.
There is no guarantee that an appeal will definitely take place and the Supreme Court is expected to make a decision on the potential appeal within the next month or two.
Last month, the Court of Appeal overturned a 2015 employment tribunal that found former Mencap care worker Claire Tomlinson-Blake was entitled to receive the national minimum wage for each hour of sleep-in shifts completed, plus six years of back payments.
Charities had previously typically paid sleep-ins a flat rate of between £35 and £45, plus an hourly rate for any time spent providing care rather than being asleep.
Mencap estimated that the tribunal ruling would have cost it £20m and the wider care sector £400m if it had not been challenged.
The ruling also prompted HM Revenue & Customs to begin writing to social care providers to inform them that they could stop calculating the amount they owed in back pay to sleep-in care workers.
HMRC had set up the Social Care Compliance Scheme to enable social care providers to identify what they owed in back pay and pay off the arrears before February 2019.
But Unison said at the time of the Court of Appeal’s verdict that the decision not to count sleep-in shifts as working time was "wrong, and is at odds with legal precedents and a common sense understanding of what counts as work".
Dave Prentis, general secretary of Unison, said at the time that sleep-in shifts "involve significant caring responsibilities, often for very vulnerable people" and the government had to do more to fund social care.
"That’s why it’s such a disgrace that workers have been paid a pittance for sleep-ins, with some getting just £30 for a ten-hour shift," Prentis said.
Commenting on Unison’s application to appeal, Rhidian Hughes, chief executive of the Voluntary Organisations Disability Group, said: "Government must provide clarity on future arrangements and the funding for essential overnight support.
"We remain committed to securing a solution that recognises the valuable contribution that social care workers make and at a level that ensures services are sustainably funded."