Hundreds of staff are to lose their jobs with the Scottish Environment Protection Agency (Sepa) after refusing to accept new pay and conditions.
Staff will be told their current contracts are terminated
About 570 employees will have their contracts terminated after failing to agree to the new terms.
This represents 43% of the total workforce at the Stirling-based agency which has 1,330 employees.
The public sector union Unison accused Sepa of "behaving like the worst Victorian mill owners".
Under the new contract, about 130 workers will have their pay frozen to bring wages in line with the new pay grading system.
Sepa said the new arrangement benefited about half of the agency's lowest paid staff and insisted that nobody would be made redundant.
A spokeswoman added that the move was being made to meet legal requirements under equal opportunity legislation.
The notices of dismissal, which will be issued on Tuesday, will be accompanied by an offer of re-engagement on the new terms and conditions, the spokeswoman said.
A Unison spokesman said: "Unison will not accept such dictatorial behaviour and will be discussing ways to counter Sepa's latest actions using all available means including industrial action where appropriate."
Although no immediate pay cuts were involved, about 130 employees, 10% of staff, would not receive rises in the near future.
Their pay "will be temporarily held back in order to bring their salary within their new pay grade", the agency said.
A spokeswoman said: "At lunchtime on Friday, 758 of Sepa's staff (57%) had accepted the voluntary pay offer.
"The remaining staff who have not accepted the offer will receive notice on 4 March that their existing contracts of employment will be terminated at the end of May.
"These notices of dismissal will be accompanied by an offer of immediate re-engagement on the new terms and conditions."
A spokesman for the Scottish Government said the issue was "an operational matter for Sepa".