Litigation and courts have been important arbiters of labour policy reforms aimed at redressing Japan’s growing social inequality. This article considers seven lawsuits brought by non-regular workers, who sought to use Article 20 of the 2012 Labour Contracts Act to gain equal pay for equal work. All seven cases reached Japan’s Supreme Court amid Abe Shinzō’s 2018 labour reforms. The Court’s interpretations reaffirmed employer discretion in categorising employees as a reasonable principle, albeit one which limits the law’s power to redress wage inequality. However, the Court also found the non-provision of various minor benefits to be unreasonable. These outcomes evince a pattern in which litigation marginally transforms reformed labour policy into institutional support for greater equality of compensation and benefits between workers of different statuses. More than advancing equal pay for equal work, the outcomes of these cases support recent government-industry campaigns to boost productivity by encouraging increased use of job-based treatment and diversifying Japan’s employment system.