Unison successfully argued that these fees prevented workers getting access to justice, especially low-paid workers.
The Unison campaign has lasted four years, and the ruling is a direct result of the union's campaign.
The government will now have to repay all those who were unlawfully charged for their cases.
The government introduced these fees in 2013, which prevented many cases from reaching tribunal, as the number of cases was reduced by 79% over three years.
The Supreme Court ruled that fees are indirectly discriminatory to women, and that the government was acting unlawfully and unconstitutionally when it introduced the fees. Discrimination cases were more expensive for claimants because of the complexity of the case, which meant that hearings took longer. This was indirectly discriminatory because a higher proportion of women would bring discrimination cases.
Unison general secretary Dave Prentis said:
“The government is not above the law. But when ministers introduced fees they were disregarding laws many centuries old, and showing little concern for employees seeking justice following illegal treatment at work.
“The government has been acting unlawfully, and has been proved wrong – not just on simple economics, but on constitutional law and basic fairness too.
“It’s a major victory for employees everywhere. UNISON took the case on behalf of anyone who’s ever been wronged at work, or who might be in future. Unscrupulous employers no longer have the upper hand.
“These unfair fees have let law-breaking bosses off the hook these past four years, and left badly treated staff with no choice but to put up or shut up.
“We’ll never know how many people missed out because they couldn’t afford the expense of fees. But at last this tax on justice has been lifted.”Fees could be anywhere between £390 and £1,200. Unison covered the cost of members' cases, but there was a very sharp drop in tribunal cases as a result of the fees being introduced.