PCS and the Prison Officers Association have launched legal action against the newly imposed civil service redundancy scheme, known as the civil service compensation scheme (CSCS).
The unions have made a claim for a judicial review, which challenges the decision of 22 December to introduce a new civil service compensation scheme - reducing redundancy benefits by up to a third.
The claim seeks a declaration that the new scheme and the changes to the law - called the Superannuation Act 2010 - which were rushed through parliament in the autumn, are incompatible with the Human Rights Act.
Following the submission of their case the unions are now waiting for a response from the Cabinet Office and a date for a hearing in the High Court.
Last year PCS won victories in the High Court over the previous government's attempt to reduce CSCS benefits.
The parliamentary joint committee on human rights, scrutinised the superannuation bill as it was debated by politicians, and concluded that it interfered with the human rights of civil servants.Legal action gets a boost after overwhelming ballot result
Prison officers massively reject redundancy cuts
Protest against the cuts at the March for the alternative in London on Saturday 26 March
Watch Lorraine on the bus telling her fellow passengers about 26 March demo
Watch the PCS video - 'Protect public services'