Up to 100 jobs are set to go as part of a £60 million cost-cutting plan.
East Sussex County Council announced the losses as members agreed their budget for the next year.
Union leaders and campaigners said the council hadn’t done enough to try to avoid job losses.
Mark Turner, from the GMB, said: “I think councils should be looking at making efficiency savings before cutting jobs.
“In some cases I don’t think they have done this. We will do everything we can to protect those at risk.”
The council also confirmed that council tax would be frozen for a third consecutive year in what it called a “budget for growth”.
Keith Glazier, the deputy leader of the council, said that councillors were forced to make “very tough choices” as part of the budget.
He added that local authority schemes such as the £94 million Bexhill to Hastings link road and the go-esussex broadband initiative would help boost the local economy.
Protest Road protesters gathered outside the meeting in number to oppose the road building plan.
A spokeswoman for the group described the project as a “colossal waste of money”.
She added: “If they weren’t going ahead with this ill-thought out project then they wouldn’t need to be cutting jobs. It’s ridiculous.”
Mr Turner added: “Any job losses are unacceptable.
“We will fight to save anybody made redundant.
Councillor Glazier said: “Our budget has now been approved and we promise to continue to boost the East Sussex economy.
“I’m delighted that we’ve frozen council tax for the third year in a row. It is so important that we help people as they try to manage their household budgets where every pound counts.”
See the latest news headlines from The Argus:
- You've stolen my life: Brighton woman tells shocking story of online 'catfish' impersonator
- No more Punch and Judy show
- Eubank Junior aims to step out of the shadow of his world boxing champ father with victory tonight
- Driver uninjured after car crashes into lamppost
- Sea and river search launched