Three hundred staff at the social care charity Turning Point have claimed unfair dismissal as part of a long-running dispute over new terms and conditions.
The charity began moves in November to sack its entire 2,600-strong workforce and re-employ them on new contracts in a bid to reduce costs.
The trade union Unite said that staff were dismissed and then re-employed in March on lower salaries and poorer terms and conditions. It said some had lost up to £6,000 a year from their wages.
Unite has now made a claim of unfair dismissal to an employment tribunal on behalf of 300 staff.
Jamie Major, regional officer for Unite, said: "It is no wonder that staff have joined together to take legal action against the charity by lodging a claim with an employment tribunal. What makes staff so angry is that these attacks on good people who provide crucial services to the most vulnerable in society are not being driven by financial difficulties, but by an increasing free market ethos in the not-for-profit sector."
He said that some of the charity's workers might have to resort to using food banks. The charity's actions were "morally wrong", he said.
"It’s now up to the tribunal to decide if Turning Point has broken the law," he said.A spokeswoman for Turning Point said that it remained committed to maintaining the basic salary level for all employees, and it had raised the basic pay for some front-line staff.
"Unite has previously acknowledged that Turning Point has not created the current difficult economic environment that has made these changes necessary," she said. "The changes were not made lightly and were made to protect jobs and services.
"We are working with all our staff through these changes and appreciate their ongoing commitment to providing a high level of specialist service to those who rely on our consistent support."
The spokeswoman said that the changes to terms and conditions were made in relation to "various enhancements, including those for unsociable hours, much of which is no longer paid within the market, and were not about pay cuts".