The closure of a food factory and the loss of 900 jobs will be a "calamity" for a town, a union said.
Union representatives said Kerry Foods in Burton-upon-Trent, Staffordshire, was the town's biggest employer.
It announced the closure on Monday, the result, according to Unite the Union, of the company losing a contract to supply ready-made meals to Tesco.
Kerry Foods said its priority was to "support all employees affected" and will meet with Unite on Fiday.
Operations would stop from the start of September, a spokesperson said.
Unite's regional officer Rick Coyle said the closure was "a crushing blow for the regional economy".
"The problem going forward is that there are not that many well-paid jobs in Burton and the vicinity to replace those that will be lost at the end of August," he said.
Unite has been in touch with brewer Molson Coors, the town's second largest employer, to "explore employment opportunities there", Mr Coyle said.
Mr Coyle estimated "90% of the work in the factory" was production for Tesco and there was not enough other work to sustain the factory after the end of the contract with the supermarket giant.
Kerry Foods - which has 18 factories across Ireland and the UK - held the contract with Tesco for 19 years before it went to another supplier in October.
Mr Coyle said workers were "heartbroken" when they were told the news on Monday and "the looks on people's faces is not something I'll forget".
Management had assured staff they had tried to save the factory, he added.
Burton's Conservative MP Andrew Griffiths said he was "disappointed and saddened" to hear of the closure.
"This will come as a great shock to all workers at the site who have provided dedicated service, and this closure is no way their fault," he said.
He said planned to meet Business Secretary Greg Clark later on Tuesday and hoped to raise the closure in the House of Commons to "minimise the impact of this very sad news".
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