Teaching assistants could take industrial action after councillors agreed to a change of terms and conditions in the contracts of 2,700 workers.
Durham County Council has said the amendments, which were agreed today, will make it fair across the workforce, giving them pay for only the hours they work.
But union officials say the change, which will see them change from 52-week working to term-time only working, will result in a pay cut of almost a quarter of wages for the workers.
Councillor Jane Brown, cabinet member for corporate services, said: "These proposals are aimed at ensuring fairness and parity across our workforce.
"They are about ensuring that teaching assistants, like all other council employees, are paid only for the hours they actually work.
"The current contract arrangements for teaching assistants represent a significant equal pay claim risk to the council and we have an obligation to address this in order to protect public finances.
"Despite every effort to reach a collective agreement on this matter with staff and trade unions it has unfortunately not been possible to achieve this to date.
"The external legal advice and the advice that we have from our statutory officers is clear and, while this is not a position we would wish to be in, councillors have now agreed to introduce these changes by ending existing contracts and replacing them with the amended ones."
Unison has condemned the decision of Labour-controlled council to "forcibly impose a less favourable" contracts and says it could result in a drop in wages by 23%.
Regional officer Helen Metcalf said: “We are bitterly disappointed with the decision taken by the authority to forcibly impose a less favourable contract on teaching assistants through the process of dismissal and re engagement.
"This is unprecedented for a Labour controlled authority and we believe that this decision has the potential to change the future political landscape of County Durham.
"Our members have already indicated, in a consultative ballot, that they overwhelmingly reject these proposals, when 95% voted against the proposed changes.
"This is a devastating blow for the 2,700 teaching assistants in the county, who now face being driven into poverty and relying on food banks through losing £200 - £400 per month of their salary.
"Now that the authority has taken this decision we are left with no option but to lodge a formal dispute and ballot our members for industrial action.”
The council said the proposals were developed following "strong independent legal advice" confirming that the current arrangements leave the it at risk of equal pay challenges that would result in significant financial cost.
A report to full council strongly advised councillors of the risks of not making the proposed changes and of its duties in relation to financial probity and care of public funds.
The report said currently, most teaching assistants are paid for working 37 hours a week, although are only required to work 32.5 hours a week.
In addition, teaching assistants are paid for 52 weeks a year although they work only during school term time.
In addition it highlights that variations in contracts also exist within the teaching assistant group, where some hours and annual leave arrangements are different on a localised level in some schools.
Councillors were recommended to agree to the proposal for the termination and re-engagement of teaching assistants on revised terms and conditions.
The council expects to start consultation on Monday, with the effort to involve formal consultation with teaching assistants and trade unions.
Staff would be given notice of the intention to terminate their existing contracts and would be offered a new contract based on the revised terms and conditions.
Under the plans the new contracts would be brought in from January and teaching assistants affected would receive a compensatory payment equivalent to one year’s loss of salary.