Care and support workers have slammed controversial plans to change their terms and conditions.
Holmewood-based EMH Care and Support is considering a shake-up which could affect about 100 members of staff.
They currently work under NHS arrangements but may soon be asked to sign EMH contracts, resulting in pay cuts and fewer holidays.
The planned changes come as Derbyshire County Council (DCC) – which commissions EMH's care and support services – faces swingeing cuts.
EMH workers have spoken to the Derbyshire Times on condition of anonymity.
One said: "Over many, many years I've been loyal and hardworking and have earned my current hourly rate of pay.
"Now we may be asked to sign new starter contracts – but we are not new starters.
"Under these new terms and conditions I face losing at least £400 per month and some of my colleagues stand to lose more."
Another said: "Most staff could lose between 30 and 50 per cent of their wages – and that would have a huge impact on their lives."
In addition, annual leave could be cut from 8.2 weeks to 5.6 weeks and and sickness leave would be affected.
One worker said: "Some people may think eight weeks' annual leave is generous – but put yourselves in our shoes; we are looking after some of the most vulnerable people in our society.
"These planned changes are so demoralising for dedicated staff, most of whom have at least 30 years' experience."
Andy Freeman, of UNISON East Midlands, criticised the proposed changes.
He said: "This is no way to treat loyal, hardworking, highly-experienced workers.
"They will leave."
EMH has been providing care and support services to people with learning difficulties since 1990.
It also provides supported housing for people aged 55 and over and a range of other services to vulnerable people.
A leaked document seen by the Derbyshire Times states: "EMH fully recognises that the NHS terms and conditions of employment are more generous than those of EMH.
"However, the DCC change requirements are driven by the need to secure a future contract with DCC."
Joanna Grainger, executive director at EMH, which was formerly known as Enable, said: "We are working in conjunction with DCC, as the commissioning body for our care and support services, to help their efficiency programme.
"Part of this requires us to review terms and conditions of relevant employees. We are working to ensure we get the best outcome for our staff and for service users.
"Protecting staff jobs is a priority for us as well as delivering high-quality services.
"We are currently in the early stages of consultation with staff and their representatives and are committed to supporting employees as much as possible through this process."
A council spokesman added: "We are facing cuts of £12.2million to our adult social care budget and we have to make sure that we are getting value for money and that every penny we spend is providing high-quality services for Derbyshire residents.
"EMH has recognised the need to reduce its staffing costs in order to continue delivering affordable services against a backdrop of decreasing budgets.
"We have been ensured that EMH will hold an open consultation with their staff including contact with clients of our services, their families and carers."