Chief executive Roger Whiteside has warned that the business, which operates more than 2,000 sites across the UK, will cease to be profitable if sales stay at the levels seen during lockdown.
It has been confirmed that in total 820 staff will lose their jobs, although no stores are expected to close.
In a statement posted on Greggs' employee information website last week, Whiteside said: "Covid trading conditions have forced this action onto our business and we are all very saddened by the need to part company with around 820 friends and colleagues, many of whom have worked with us for many years."
He went on to say that the battle with Coronavirus 'hasn't gone away and is intensifying further' as lockdown measures continue to be in place across England, Northern Ireland, and large parts of Scotland.
Whiteside added: "At lockdown levels of sales, even after all of the mitigating action that we have taken, Greggs will not be profitable as a business and there can be no room for complacency."
Back in September, Greggs said it was in talks with staff to cut hours to try to minimise job losses when the furlough scheme was originally expected to end in October.
Whiteside told reporters at the time: “Some stores have staff hours which are just off what’s needed for current demand. But others are a long way off and will need significant change.”
Greggs is one of a number of national chains that, having installed extra Covid-safe protocols, has pledged to keep its entire estate open throughout the second country-wide lockdown in England that began on 5 November and is set to last until at least 2 December.