The NHS in Scotland is facing a multi-million pound equal pay claim from female workers.
Union officials have submitted grievance letters to seven health boards demanding back pay for thousands of women employees.
The move follows a campaign on behalf of low-paid female council workers, which has prompted local authorities to offer settlements, reports The Herald newspaper.
It is estimated Scotland’s 32 councils may have to find £500m in back pay to make up the difference between the wages of women employees and men in equivalent posts.
The claim by the GMB and Unison unions currently includes women employed as nursing auxiliaries, cleaners, caterers, laundry workers and clerical assistants.
The unions are asking health boards to redress the imbalance that existed before staff were moved onto the Agenda for Change pay system.
Unison said it hoped to negotiate a deal with health authorities, rather than resort to legal action which could take a long time to resolve.