Steel giant Tata is to axe 110 jobs at its main Corby plant.
Michael Leahy, general secretary of the Community union, said: "This is a massive blow for the workforce in Corby who have done everything expected of them to keep the site viable.
"The impact on the local community and families will be particularly hard.
"We are arranging an urgent meeting with Tata Steel Tubes to demand assurances there will be no compulsory redundancies and to explore all other options available.
"We also want a clear commitment from Tata Steel to the long-term security of the site at Corby."