Half of the staff at arbitration body Acas are taking their employer to tribunal over indirect sex discrimination.
The Public and Commercial Services Union is bringing a single action on behalf of 464 of its members in a dispute over Acas' length of service payments.
This week Acas, which employs about 800 people, launches its arbitration scheme which is designed to provide a fast and confidential disputes resolution process and help cut the number of cases going to employment tribunals.
Jim Hanson, spokesman for the Public and Commercial Services Union, said the dispute centres on Acas' pay levels, which are linked to length of unbroken service rather than the experience and contribution of individuals.
Hanson said the union's members are claiming indirect sexual discrimination against Acas because women who took career breaks to have children were penalised under the system.
"Someone who has served 10 years and took maternity leave in the middle might not be able to qualify for the length-of-service increment, even though they have much more valuable experience than someone who has been serving their time for 25 years."
The union's action, which is due to be heard at a tribunal in Birmingham at a date yet to be set, will include eight test cases, one for each of the Acas pay grades.
Most of the cases involve female staff, but the union is also representing a number of men.
John Taylor, Acas' chief executive, said, "Acas is an employer in its own right similar to many others in the public sector.
"We have a problem with our pay structure caused over a number of years by the way in which pay deals have impacted on the organisation.
"We therefore called in an external consultant to advise us. It is crucial we get the pay right for all of our staff. We intend to have a much improved system in place by the end of the year."
Background to Acas
- Acas, which celebrated its 25th anniversary in 1999, was set up t