Up to 211 jobs may go as Fletchers’ Sheffield bakery is "reshaped", following a strategic review.
The review identified a range of loss-making product lines that may be axed, if customers agree.
Production for the remaining range would be moved to a five- day week from the current 24/7 shift patterns.
A 90-day consultation with the site’s 550 staff has started. The plans would impact all functions, areas and departments.
Employees are also being consulted over changes to the full range of terms and conditions. If proposals go ahead, the new working arrangements would start from 10 December 2007.
A spokesman for owner Vision Capital said the bakery, bought from Northern Foods last year, needed "urgent action" to provide a platform for growth, after several years of "significant losses".
Some £5m capital investment was planned at Fletchers’ sister manufacturing sites in London, Barnsley and Manchester, which had also been reviewed, he added. No redundancies were planned.
Peter Williams, general manager at Sheffield said: "We will be consulting fully with all potentially affected employees and keeping them in the picture. These proposals are vital to secure the future of Fletchers Bakeries in Sheffield."
Merlita Bryan, district secretary for the Bakers, Food & Allied Workers Union (BFAWU), said the company had met with unions this week and was due to hold another meeting on Monday. She said some 150 job losses were expected on the manual and driving side.
"Moving to a five-day week, plus changes to terms and conditions, which we expect to include overtime and holiday pay, is a double whammy. This is another major blow, following on from floods and a series of setbacks."
Fletchers suffered damage in a fire in July 2006, while in February, 74 jobs were axed.