Dozens of Cadbury's workers will protest outside the company's headquarters in Birmingham in the hope they can save it from a hostile takeover.
The confectioner is facing a hostile bid from US-based food company Kraft.
However, the union Unite, which represents many of the firm's 6,000 workers in the UK and Ireland, believes its shareholders should resist selling up.
About 100 workers will hold a demonstration from 10am on Tuesday.
Len McCluskey, Unite assistant general secretary, said: "There is serious and growing worry, stretching from the shop floor to the wiser heads on the City trading floor, about what the Kraft offer and any ensuing bidding war could mean for Cadbury.
"Cadbury is a great UK success story and it was and is not for sale. But suddenly, a hostile bid and swarming speculators has thrown its future, its investment plans and the jobs of thousands of workers here and in Ireland up in the air."
Unite has also launched an online petition at www.welovecadbury.com.