Identifying and addressing the factors influencing the within-firm pay gaps has become a pressing issue amidst the widening global income inequality. This study investigates the impact of corporate ESG ratings on employee income and pay gaps using data from Chinese-listed companies between 2017 and 2021. The results suggest that ESG ratings significantly increase employee income. Further research indicates that ESG ratings exacerbate the within-firm pay gaps and income inequality due to the varying bargaining power among employees. This effect is particularly pronounced in non-state-owned and large-scale companies. This is also true for all kinds of companies in traditional and highly competitive industries. However, reducing agency costs and improving information transparency can help vulnerable employees with weaker bargaining power in income distribution to narrow their pay gaps. The research findings offer important insights to promote fair income distribution within companies and address global income inequality.