Hundreds of jobs in Lincolnshire are in doubt at one of the county's biggest food companies because of the coronavirus pandemic
Bakkavor in Spalding blamed the virus and a bad start to the year for its plan to close one of its four factories at West Marsh Road.
The firm said it was "reviewing and reducing functional support roles" and the change affected about 500 people.
The Unite union said it would talk to the company but also consult lawyers.
In a statement the firm said: "We can confirm that we are entering into several consultations with employees at our Spalding site where we have two salads factories, two meals factories and a distribution centre.
"Over the past 12 months the salads businesses at Spalding (Factory 1 and the Deli) have come under increasing pressure due to the impact of a business loss at the beginning of 2020 and more recently the impact of the Covid-19 pandemic crisis.
"As a result, we have had to make some difficult decisions to ensure we can continue to remain sustainable in what remains a particularly difficult trading environment."
The company said it was proposing to stop operating Factory 1 and change the night shift patterns within the Deli.
"We are also proposing to change how we manage operations across the site which will involve reviewing and reducing functional support roles. There are just over 500 employees impacted by these proposals."
Mick Orpin of the Unite union said: "We will go into the consultation with an open mind and try to mitigate any possible redundancies.
"We will be going on weekly basis and working with our reps on site, but we are questioning the timing of it.
"Hopefully that we can have meaningful consultation, but we will take a legal view on the timing of the proposals."