Part-time soldiers from Northern Ireland losing their jobs next year are to take the British government to an industrial tribunal.
About 1,100 Royal Irish Regiment members are alleging discrimination after being denied thousands of pounds worth of privileges including pension provision.
Soldiers are expected to claim the Ministry of Defence is breaking European law in denying them equal rights to full timers.
Democratic Unionist MP Jeffrey Donaldson said: "They are taking cases against the MoD.
"This is about pensions. They are saying that they have pension entitlement under the European Union and part-time workers' regulations.
"It states that they are entitled to pension provision and therefore the MoD is in breach of EU law." The disgruntled troops have lodged papers with the industrial tribunal in Belfast.
If they are successful military chiefs could face a multi-million pound bill. The Ministry of Defence announced in August 2005 that the two Northern Ireland-based battalions of the RIR would be disbanded by August 2007.