The union's Derbyshire branch is seeking legal advice because the council wants to stop paying un-sociable hours and weekend pay to staff who are off sick, abolish sleep-in pay for managers in homes for older people, and re-grade night care assistants. Most sick pay will be based on weekly contracted hours.
The council said this is part of the single status agreement intended to address long-standing anomalies between the conditions of manual and non-manual staff.
The changes will affect unit and deputy unit managers, night care assistants, day care assistants, cooks, kitchen assistants, domestic staff and relief staff.
'There has been a long consultation over this whole issue with the unions,' she said.
Staff have until 27 April to sign the contracts, or face losing their jobs.
Unison branch secretary Peter Moore said residential staff faced greater levels of sickness such as injury, back pain, infection and stress. A cut in sick pay would dramatically affect their income.
He said: 'The national single status agreement clearly states that the costs of cutting hours were not to be offset against pay and other working conditions.'