Veolia, which is contracted by councils to carry out bin collections, issued HR1 redundancy forms to some 1,200 workers last week.
Bosses want to force the workers to sign new contracts that would change their conditions.
Veolia workers perform a variety of jobs for around 100 councils.
The staff work collecting bins and recycled material from homes, as well as carrying out street sweeping.
After the GMB union threatened a national strike ballot, the company withdrew its redundancy threats.
But the company may still try to force worse terms and conditions on workers.