The BBC reports the Supreme Court has upheld an earlier court ruling that lower-paid shop staff, who are mostly women, can compare themselves with higher paid warehouse workers, who are mostly men.
The judge stressed the ruling did not mean the 44,000 claimants had won the right to equal pay.
However, they are now free to take further action.
Lauren Lougheed, a Leigh Day lawyer representing Asda store staff, said: “We are delighted that our clients have cleared such a big hurdle in their fight for equal pay.
“Already an employment tribunal, the employment appeal tribunal and the Court of Appeal ruled that these roles can be compared, and now the Supreme Court has come to the same conclusion.
“It’s our hope that Asda will now stop dragging its heels and pay their staff what they are worth.”