Workers at Anglian Water are to stage a 24-hour strike and a work to rule in a dispute over pay.
GMB union members at the company have voted to walk out on 12 June. They will also work to rule and withdraw goodwill. The action follows a warning that shift changes could lose staff up to £2,500 a year in pay.
The workers maintain sewage facilities in Essex, Hertfordshire, Bedfordshire, Norfolk, Suffolk, Cambridgeshire, Northamptonshire and Lincolnshire.
Industrial action could impact on the supply of clean water, the clearing of sewage and on the safe discharge of sewage into rivers, said the GMB.
Michael Ainsley from the GMB said, “So far Anglian Water has shown no willingness to negotiate and determined to force a strike.”