The Supreme Court will decide next month whether Sheffield Council discriminated against female care workers by excluding them from a bonus system available to staff in roles largely occupied by men.
Under Sheffield's current pay structure, gardeners and street cleaners, who are mostly male, receive bonus payments to "boost productivity".
As a result, they are paid up to 38% more than those in female-dominated comparable jobs, such as care work and catering.
The council maintains the pay difference has nothing to do with gender. But, at a Court of Appeal hearing last year, 90 care workers were among those to successfully argue that the pay structure was sexist.
Lady Justice Smith said at the time: "Where the statistics show that the pay practice has produced an adverse impact on women over a long period, it will be difficult for an employer to show that the adverse impact had nothing to do with sex."
Sheffield Council has challenged the ruling and the case will now be heard in the Supreme Court. The final outcome could have implications for other employers who set different pay levels for traditionally male or female roles.
Unison, which is backing the care workers and dinner ladies in the dispute, said it had around 40,000 similar equal pay cases that would likely be affected.
Many of these claims were issued after the original employment tribunal hearing in 2007, so were not party to the current appeal.
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Sheffield judgement pinpoints gender pay differences