Workers at Northumbrian Water are set to strike from 20 October over the introduction of a Career Average Revalued Earnings (CARE) scheme.
The GMB and Unite unions have argued against the switch away from a final salary scheme which were proposed in January this year.
Initially Northumbrian Water said it would contribute 19.5% and members would add 8% but has now said these were no longer correct.
GMB regional officer Maxine Bartholomew said: "Northumbrian Water call themselves an ethical company. But they choose to increase the shareholders' dividend while proposing pension cuts to the workers who make them these massive profits. According to the company's last financial statement, Northumbrian Water had a £384m operating profit. How much profit is enough for this company?"
Unite officer Pat McCourt added: "It's more than 30 years since there has been any industrial action with this company. The company is hell bent on forcing our members into taking this industrial action to protect their pensions and their income in retirement. After all pensions are just deferred pay and the company are cutting that while siphoning off profits abroad."
NWG Wastewater director and chair of the consultation group Richard Warneford said: "Almost all water companies have already made changes to their defined benefits pension schemes. We are in the minority of companies being able to keep a defined benefits scheme open and we are providing our employees with one of the best schemes in the water industry.
"We regret that in response to changes to our final salary pension scheme, some of our union members have decided to take industrial action not involving a strike.
"Our priority will be to safeguard our service to customers and protect the environment and we have contingency plans in place."
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