Birmingham city council wants to scrap allowances paid to staff that work weekends or evenings.
Many of those set to lose out are already low paid.
Care workers who provide support for the city’s elderly and disabled will be particularly hit.
This comes on top of plans announced in February to shed 2,000 jobs and impose pay freezes.
The Unison union said the cutting the allowances could result in pay cuts of up to a third. It means an end to double time for Sunday working and time and a half for Saturdays.
Cleaners, librarians and leisure centre workers would also be affected.