Computer manufacturer Evesham Technology sacked around 150 workers on Friday 3 August without any warnings.
The employees were split into two groups, one led up stairs where they were told they still had a job, and the others were told to go home.
Employees working off site were told their fate by a text message.
GMB union members demonstrated outside the company on Wednesday of last week. Workers were amazed to find agency workers starting work at Evesham.
The union is urging all staff still employed by Evesham Technology to join it in case the same thing happens to them.
Evesham Technology is a major computer manufacturer. It supplies the latest HD Ready LCD TV’s, satellite navigations and PCs.
Martin Hird, senior organiser with GMB, said, “It is an outrage that the company has employed agency workers just days after dismissing employees who are still owed wages and holiday pay.
“They have received no notice pay or redundancy payment and the company now brings in outside labour to do their work.”
Jason Singleton, a GMB member and one of the sacked employees, said, “I was told on Friday 3 August by a colleague within the company of the dismissals.
“I had received no information from my manager. I spent the next few hours trying to find out if I still had a job.
“Finally at 7.30pm I was told that I would not be required for work at the factory.
“I have been employed by Evesham Technology for nine years in several key positions, I do not know how or why I was selected and I still haven’t received any money owed to me by the company.”