Asda workers have lost a three-year battle with the retailer over new pay terms they claimed amounted to constructive dismissal and an unauthorised deduction of wages.

In 2007, when Asda unified two pay structures, 8,700 workers refused to transfer to the new regime voluntarily. Seven hundred workers took the case to tribunal, arguing Asda could not impose changes to an employee's terms and conditions without their consent. They lost their initial case and six workers went on to appeal although only one argued she earned less than before.

Last week in a case that hinged on whether a clause in the staff handbook allowed Asda to impose changes without consent of the workforce the Employ­ment Appeal Tribunal said the retailer had followed all necessary procedures.

While the tribunal added that the law normally required the consent of the workforce, it ruled in Asda's favour because of the steps the retailer had taken to ensure staff who transferred earned no less than before.

"There is no contention that [Asda] acted capriciously, or arbitrarily, or in any way which breached mutual trust and confidence, in imposing [the new regime] in August 2007," the tribunal ruled.

"We are really pleased we were found to have acted lawfully," said Asda, adding that many staff were better off as a result of the change, and those who earned less as a result were paid a supplement to cover the difference.