Unite, the country’s largest union, has 530 members working at the Smethwick site.
Unite’s national officer for food Julia Long said: “We had a positive and constructive meeting with the company’s management on Monday 10 April and have made a commitment to prepare a set of proposals to save as many jobs as possible.
“We will be presenting our proposals to the management when we meet them again at Smethwick on Friday 21 April.
“One of the areas we will be investigating to mitigate job losses is redeployment across the firm’s other operations in the West Midlands, as it was made clear that the Smethwick site will close.
“We won’t enter into speculation as to how many jobs may be saved.
“This announcement has been devastating news for the company’s workforce at the Smethwick site and their families. Unite is offering our members maximum support at this very difficult time.
“During the 45-day consultation period, we will be fighting our members’ corner during further meetings with management to achieve the best outcome possible in terms of future employment opportunities.”