EIGHT years after Britain emerged from recession, average real earnings are still below their peak. But measly pay is not the only thing squeezing workers. Since 2013 employees who think they have been wronged by their employer—underpaid or dismissed unfairly, for instance—have had to pay up to £1,200 ($1,500) to go to an employment tribunal, which was previously free. A challenge to the legality of such fees came before the Supreme Court on March 27th. A judgment is expected by the summer.

Since the decline of trade-union membership in Britain, the employment-tribunal system has been the main mechanism for enforcing individual employment rights. In 2012-13 there were roughly 190,000 tribunal claims, equivalent to one for every 130 or so employees. After fees were introduced the number of claims dropped by about 70%. There were only around 60,000 in 2014-15.

The government has welcomed the decline as evidence that bogus claimants are being deterred. “Like Japanese knotweed,” one government minister wrote in 2014, “the soaring number of tribunal cases [was] squeezing the life and energy from Britain’s wealth creators.”

But a paper in the Modern Law Review by Abi Adams and Jeremias Prassl of Oxford University suggests a different interpretation. The authors argue that the fees prevent genuine claimants from enforcing their employment rights. In many cases the expected payoff is lower than the fee for starting the tribunal—which is not necessarily refunded even if the claim is upheld. The authors calculate that abandoning even a claim guaranteed to succeed is the rational response for 35-50% of would-be claimants.

Worse, there is little evidence that the fees have deterred only frivolous or mendacious claims. If that were the case one would expect the success rate of claimants to have risen. Instead, since 2012-13 the proportion of complaints that are struck out or dismissed has roughly doubled. It may be that people with small but legitimate grievances have been deterred, whereas those who feel confident enough to game the system have gone ahead.

Even if convinced by such arguments, the Supreme Court may not recommend the abolition of fees entirely. A report last year from the Justice Committee of the House of Commons acknowledged that a contribution by users to the costs of operating courts was not objectionable in principle. A recent government review made a similar argument. Yet Ms Adams and Mr Prassl argue that the steepness of the fees makes them a “disproportionate restriction on litigants’ right of access to the employment tribunals”. That is bad not just for litigants but for Britain’s labour market generally.