Civil service unions are seeking a judicial review over the government’s failure to consult on pay. Three unions, representing 200,000 public employees, have accused ministers of never intending to consult staff before offering a new pay cap of 1.5%.

The FDA, Prospect, and the Public and Commercial Services (PCS) unions said they were making the unprecedented move after government promises to negotiate failed to materialise.

Solicitors for the government are expected to claim that no such undertakings were made and that the government is not obliged to consult with the unions.

It is the first time that public-sector unions have sought a judicial review over the government’s failure to consult. The move reflects a deep frustration among civil servants who have seen other public employees receive pay increases after consultations.

The FDA general secretary, Dave Penman, said the government’s consultation process on pay had been shambolic. “This, more than anything, demonstrates the perilous state of industrial relations in the civil service,” he said.

Mike Clancy, permanent secretary of Prospect, said the refusal to consult in any meaningful way demonstrated a disdain for hundreds of thousands of civil servants. “By treating civil servants differently and worse than those employed in other parts of the public sector, the government has shown how little they value their vital contribution,” he said.

Mark Serwotka, general secretary of the PCS, said: “Not content with reneging on its commitments to engage in consultation on an issue as fundamental as our members’ pay, the government is now adding insult to injury by claiming it never intended to consult in the first place. This shambolic state of affairs cannot go unchallenged and we will now pursue this matter to the high court.”

The legal case will concern some meetings held between union officials and ministers in May and June 2018.

Whitehall guidance, published on 25 June, told departments to limit average pay awards for government workers in 2018-19 to a range of 1%-1.5%, which represented a lower settlement than that for many other parts of the public sector. NHS workers, police, local government workers, teachers and prison officers, have been covered by pay review bodies or have held meaningful negotiations with the unions, insiders said.

The civil service unions also wrote to Liz Truss, chief secretary to the Treasury, to seek an urgent meeting but said they did not get a response.

Last year, the PCS successfully launched a judicial review over the government’s civil service compensation scheme, which led to changes to the guidance. The former cabinet office minister Ben Gummer was found to have acted unlawfully by excluding some unions from negotiations about redundancy terms.

Asked to respond to the latest move and the claim that the government had broken a promise to consult unions over pay, a government spokesperson said: “Civil servants do an outstanding job supporting the delivery of public services right across the country. This year’s pay guidance provides greater flexibility for civil service pay, striking a balance between rewarding our hard-working staff while ensuring good value for the taxpayer.”