Tens of thousands of women who claim they are paid less than men doing comparable jobs could benefit when the supreme court examines a test case next month.
The battle for equal pay led by dinner ladies and care workers in dispute with their employer, Sheffield city council, will be heard in an attempt to clarify the complex law on what amounts to indirect sex discrimination in pay.
The three-day hearing before five justices in mid-October is the first time the supreme court – established two years ago – has looked at the issue of equal pay, an area complicated by the existence of contradictory legal precedents.
The outcome could affect wages paid to workers, particularly in local authorities and the NHS where some specialised roles – such as road sweepers or carers – have traditionally been performed almost exclusively by separate groups of men or women.
The trade union Unison, which is supporting the Sheffield employees, said it had up to 40,000 cases that could be affected by the court's ruling.
The Sheffield council case, Gibson and others v Sheffield city council, started in an employment tribunal and has been working its way up the appeals process.
The court of appeal last year found for the dinner ladies and carers, ruling that productivity bonuses granted to male street cleaners and gardeners, which were subsequently incorporated into their salaries, were discriminatory against women doing work of equal value.
In its ruling the court of appeal held that the men were being paid between 33.3% and 38% more than women for occupations that the council agreed were comparable.
Sheffield council had argued that an earlier decision, Armstrong v Newcastle upon Tyne NHS hospital trust, set a precedent that bonuses had nothing to do with gender but were paid to boost productivity. It claimed that the predominantly female jobs could not be measured or rewarded in a similar way and therefore the differences in pay did not need to be objectively justified.
The women, however, maintained that the European court of justice case of Enderby v Frenchay health authority, dating back to 1993, was the relevant authority and that the council had a legal responsibility to provide an objective and gender-free reason why dinner ladies and carers were paid less.
The judges agreed. Giving his ruling in the appeal court, Lord Justice Pill said: "The impossibility of applying the productivity bonus to women's work, carefully reasoned by the [employment] tribunal, is genuine enough but that does not remove the sexual taint from the operation of the scheme.
"The scheme has a disparately adverse effect on women's work as compared with men's work and the sexual taint is present. It must be justified objectively if the employers are to succeed. The opportunity to justify is a sufficient protection for employers."
Lady Justice Smith agreed, pointing out that: "Where the statistics show that the pay practice has produced an adverse impact on women over a long period and where the statistics are convincing, it will generally be difficult for an employer to show that the adverse impact had nothing to do with sex."
Sheffield council has now taken the case to the supreme court. Ben Patrick, Unison's in-house solicitor who is preparing the case for next month's hearing, said: "The central issue is whether the council should be required to justify differences in pay.
"It's an indirect discrimination argument based on statistical comparisons. The question in the supreme court is whether given a statistical case of discriminatory pay the employer is required to objectively justify the differences in pay between men and women.
"We are saying that Armstrong is inconsistent with Enderby. The indirect discrimination pay cases being considered are virtually indistinguishable from each other so it could have the effect of forcing a large number of local authorities to reconsider their defences."
Most of the outstanding equal pay cases date back to a period before the introduction of the Equality Act in 2010, which essentially removed the employers' ability to rely on the Armstrong defence. "There are still tens and tens of thousands of cases coming through the tribunal system," Patrick added. "Unison is running equal pay claims for about 40,000 of its members. Most are in the health sector or local authorities."
Sheffield city council was said to be facing compensation payments of £20m following last year's judgment.
