The Public and Commercial Services (PCS) union's High Court challenge to what it believes are "unlawful" government changes to the civil service redundancy scheme begins today.
The two-day judicial review follows the Cabinet Office's announcement in February that compulsory redundancy packages will be capped at £60,000 for those earning less than half that amount, affecting four-fifths of the workforce. Those earning more than £30,000 will see redundancy payments cut from up to three years' pay to a maximum of two years' pay.
While the changes to the redundancy terms were accepted by the five other trade unions representing public sector workers after changes were made to the original proposal, the PCS continued to oppose the move.
It sought the judicial review, arguing that the Cabinet Office was wrong to make "detrimental changes" to the civil service compensation scheme without agreement.
The union believes that, under the 1972 Superannuation Act, the government needed to implement the cuts to the redundancy scheme with the agreement of civil service trade unions representing the majority of staff (it represents 270,000 workers, compared to the 100,000 covered by the other five unions).
If the judicial review is successful, it would make the new arrangements illegal and invalid.
PCS general secretary Mark Serwotka said: "We have always accepted that changes had to be made to the scheme, but all we ask is that they are fair and reasonable, and that we can make them by agreement.
"We believe we have a strong case but this is not our only avenue. PCS members have already shown they are prepared to take industrial action to defend their jobs and the public services they provide, and we will be knocking on the door of the next government very early on to remind them that they need to reach an agreement with us."
Gus O'Donnell, head of the Civil Service and permanent secretary at the Cabinet Office, has described the decision by the PCS to continue opposing the proposals as "wholly misguided".