A long-awaited equal pay lawsuit at the U.K. Supreme Court could see thousands of mostly female workers obtain better wages from the largest supermarkets and end up costing the chains as much as 8 billion pounds ($10.1 billion).

The Supreme Court on Monday will scrutinize a discrimination case brought by more than 15,000 employees who work at Walmart Inc.’s Asda stores. The group contends that they should be paid the same as workers in the company’s warehouses, who are predominantly men.

The case could redefine how work is valued for women at supermarkets across the country with similar suits pending against J Sainsbury Plc, Tesco Plc, Wm Morrison Supermarkets Plc and Co-Operative Group Ltd. The total value of the claims is around 8 billion pounds, according to lawyers at Leigh Day, who act for the workers.

Asda has insisted that its hourly pay is the same for male and female workers and that disparities only arise because the work is different in warehouses than in the stores.

The fallout from the coronavirus pandemic has put renewed pressure on equality in the labor market. But British firms have made mixed progress to narrow the pay gap since the government forced companies to disclose wage data in 2018. On average, men make about 14% more than women.

Michael Newman, a lawyer at Leigh Day, said Covid-19 should be focusing everyone on the importance of key workers, who work in stores every day.

“Why are we valuing one set more than another?” Newman said. “The job hasn’t changed; we’ve just woken up to their importance.”

The grocer appealed the case to the Supreme Court after losing in a lower tribunal, which ruled that it was fair to compare the different jobs.

“While we respect the rights of retail workers to bring this case, we fundamentally disagree with its premise and will continue to make our arguments clear,” Asda said in a statement ahead of the hearing. “Retail and distribution are two different industry sectors.”

The case has been winding its way through the courts since 2014, when about 1,000 workers first brought the claims to an employment tribunal.

If the Supreme Court dismisses the appeal, the employees will then have to prove two more points: that the different roles are of equal value and that discrimination is the reason for the pay gap.

The hearing comes as the virus-related downturn is disproportionately hurting women’s employment. According to an early April analysis by the Institute for Fiscal Studies, women were more likely than men to work in a sector that had been shut down due to coronavirus, such as retail and childcare.