The Supreme Court hearing is likely to take place in the second half of 2023.
The union is working on behalf of member Fiona Mercer. She had been in a dispute with former employer Alternative Futures Group (AFG), who intended to cut payments to care staff working sleep-in shifts. Mercer was subsequently suspended by the company.
Mercer won her case of unfair treatment in relation to strike action at an employment tribunal, before the decision was overturned by the Court of Appeal.
Strike action in the UK:
Matt Jenkin, employment specialist at law firm Moorcrofts, said the Supreme Court's decision could have big implications for trade unions and workers alike.
He told HR magazine: “The decision of the Supreme Court will be keenly anticipated. It has always struck me as odd that employers are prohibited from dismissing employees for taking part in protected industrial action, but the legislation does not prevent an employer from subjecting employees to a detriment short of dismissal, such as in Mrs Mercers case suspension and a warning, for having done so.
"I can’t see why it is necessary to make the distinction given that action short of dismissal can still have significant consequences for employees. With industrial action on the increase, trade unions and their members will be keen to see if the Supreme Court is willing to extend the protection to cover the current gap."
The Trades Union Congress (TUC) reported the UK government to the United Nations (UN) in September 2022 over its opposition to strike action, which included repealing a ban on companies using agency workers to cover for employees on strike.
Unison general secretary Christina McAnea said: “This is a chance to fix a glaring legal loophole. Employees only strike as a last resort and shouldn’t face punishment for protesting about their employer’s behaviour.
“Hundreds of thousands of workers are thinking about industrial action as they struggle to cope with low pay in the face of soaring prices. Everyone must be able to exercise their rights without fearing they’ll be treated unfairly for standing up for themselves at work.”