Northern Ireland Water staff are set to take industrial action after talks failed to resolve disputes over changes to the pension scheme.
The strike will take place on Monday December 22 and is likely to lead to 'supply disruptions'.
According to GMB, the action is over attempts by the government owned company to scrap the current pension scheme and bring in new proposals that will cost many members up to £100 per month.
NI Water has warned that unless the planned industrial action by Trade Unions is averted, customers could be 'severely impacted' suffering lengthy interruptions to their water supply over the Christmas period.
They also said that there is a significant risk that the quality of discharges from wastewater treatment works to water courses will be adversely affected.
NI Water CEO Sara Venning said: “Whilst I am determined to remain engaged with Unions to try an avert this industrial action I am concerned regarding the consequences for the public if it does proceed.
“We will take all possible steps to mitigate any potential impact to customers, including seeking assistance from contractors and other agencies as well as invoking our Mutual Aid arrangements with other Utilities and UK water and sewerage companies.
"Despite this, however, in the event of Unions not allowing their members to provide the normal cover in emergency situations over the Christmas period, we will have very limited in-house resources to operate and maintain our water and wastewater assets and infrastructure.
“The likely impact we will have to deal with as a consequence of this would include:
* Problems at our Water Treatment Works over the Christmas Holiday period, with potential deterioration in water quality;
* Customers in some areas may experience interruptions to supply and intermittent problems with their water pressure;
* Discharges to watercourses from some of our large Wastewater Treatment Works are likely to be adversely impacted;
* Customers are likely to encounter delays in response to problems that they report including flooding, bursts and supply interruptions.
She added: “I do recognise the right of employees to participate in action but I have made it clear to unions that it is not within the gift of NI Water to defer pension reform.
"All that will be achieved by undertaking industrial action at this time is to cause distress and potential hardship to the public. I would appeal to Unions to consider the suite of proposals which have already been put on the table and which I feel represent a fair and equitable outcome for their members, particularly at this time of budgetary pressure across the public sector.”
GMB said, talks on December 17 and 18 between the water trade unions and Minister for Regional Development Danny Kennedy, aimed at avoiding disruption to water supply and treatment services in Northern Ireland over the Christmas period, ended without agreement.
The industrial action will take the form of a work to rule including withdrawal of on-call, standby and overtime and this is likely to lead to supply disruptions as Northern Ireland Water have more than 2,700 treatment works and pumping stations to maintain.
GMB Regional Officer, Alan Perry said: “Over 1000 workers employed at Northern Ireland Water are to take industrial action from Monday 22nd December after more than 90% backed a ballot organised by the unions representing staff.
"The action, coordinated by the Water Group of Trade Unions, is in protest at attempts by the government owned company to scrap the current pension scheme. The new proposals will cost many members up to £100 per month.
"The three unions which represent staff at Northern Ireland Water met with the Minister, Danny Kennedy, on Wednesday on 17th and intense discussions continued until late afternoon on 18th. However union representatives have unanimously rejected minor concessions tabled by NI Water management.”
NIPSA Assistant Secretary, Ryan McKinney said: “The current proposals will mean that many staff will see their contributions increase by £100 per month. We heard today from workers who are worried about their ability to keep a roof over their head so they are absolutely determined to resist these changes.
The unions have set out their position to both the Minister and Northern Ireland Water and unless the pension proposals are taken off the table staff will take action from Monday. The trade unions are willing to continue with negotiations right up to and beyond the 22nd December in order to attempt to find a solution and avoid disruption to communities.”
Meanwhile in a fresh wave of strikes by health workers are to be staged in the new year amid the bitter dispute over pay.
Ambulance workers in the GMB union in England and Northern Ireland will strike on January 29 and 30.
The dispute has been raging all year after the Government decided not to accept a recommended 1% pay rise for all NHS staff.