A ruling by leading judges on equal pay compensation claims by women who worked for a local authority could have "huge implications", lawyers say.
Solicitors say the Supreme Court judgment could be a "landmark" and the most "radical reform" since equal pay legislation was introduced in 1970.
The Supreme Court decision - which will be announced at a hearing in London - follows rulings in the High Court and the Court of Appeal.
In November, the Court of Appeal said scores of cooks, cleaners, catering and care staff previously employed by Birmingham City Council were entitled to launch pay equality compensation claims in the High Court. The city council challenged that decision in the Supreme Court - the highest court in the UK - and will today learn whether its appeal has succeeded.
Judges heard that more than 170 women were among female workers denied bonuses similar to those handed out to employees in traditionally male-dominated jobs such as refuse collectors, street cleaners, road workers and grave diggers.
The court was told that that, in 2007 and 2008, tens of thousands of pounds were paid to female council employees to compensate them. More payments had also been made women who took cases to an employment tribunal.
But only workers still employed or who had recently left were eligible to make claims in a tribunal. Those who had left earlier were caught by a six-month deadline for launching claims. To get round the deadline, 174 women had started actions for damages in the High Court, which has a six-year deadline for launching claims. The city council had attempted to have those claims struck out, arguing that under equal pay legislation such claims could only be entertained by an employment tribunal.
Law firm Leigh Day & Co, which represents women trying to launch compensation claims, said the Supreme Court decision could affect "thousands of potential claimants".
"The Supreme Court will give a landmark judgment … which could represent the most radical reform to Equal Pay since the original legislation was introduced in 1970 and will have huge implications for thousands of workers," said a Leigh Day spokesman. "If the council is unsuccessful and the Supreme Court were to uphold the decision of the Court of Appeal, it would make it possible for thousands of workers to bring claims against their employers outside of the current time limitation period of six months in the Employment Tribunal."
Leigh Day said the council had lost in the High Court and the Court of Appeal. Lawyers said they were disappointed that leaders chose to appeal to the Supreme Court rather than negotiate.