Leaked documents accuse American bosses of "smashing" Cadbury's culture with the shopfloor "run by temporary managers and agency workers".
An internal document drawn up by disgruntled shop-floor workers says some employees are being "railroaded towards redundancy" and accuses bosses of a "woeful" management style.
The document was leaked to the Post just weeks after it was announced more than 200 Cadbury workers were to leave Bournville on voluntary redundancy terms, with some in line for payoffs of more than £100,000.
Unite leaders hailed the January agreement as a historic settlement securing the future of Bournville for 25 years, paving the way for a £75 million investment programme with four new production lines replacing ageing equipment.
But the new document says some shop stewards are concerned at the reported redundancy payouts and say equipment is lying idle while chocolate is being supplied from Bournville to other Mondelez plants overseas.
The document states: "Only people who fit the age profile of 55 and over with maybe 40 years plus service are being paid close to the figure stated and they are in the minority.
"The 15 European factories are being supplied by chocolate tankered from Bournville, to supply these sites, while plants lie idle at the Bournville site.
"How can Bournville be competitive with one arm tied behind its back when a basic ingredient such as chocolate is being sent abroad?
"At this present time union agreements are being ignored, people are being asked to run plants without proper training and insufficient labour, due to experienced workers being railroaded towards redundancy.
"The Cadbury culture it was supposed to protect has been smashed and the shopfloor is being run by temporary managers and ever more agency workers supplied by a company who do not support trade unions."
The document said Bournville's American owner was centred on "creating more profit from a well-established and loved product".
From a business perspective, £75 million investment to improve productivity and reduce costs is considered on the whole to be a small price to pay to leverage the profit margin of what is one of the most popular chocolate brands.
"The £75 million will appear at some point, or is this part of a relocation strategy that the workforce at Bournville suspect?," the document continued.
"Mondelez have taken a confrontational approach towards the workforce and their team briefings seem inconcise and far from transparent. The recent round of redundancies are already having an effect on the Bournville community and businesses who rely on trade from the now diminishing workforce.
"The workforce and the people of Bournville want a successful Cadbury and are prepared to work for it."
An insider said: "It is true there have been a lot of changes going on and that change impacts on people and they are sometimes upset by change.
"There have been constant negotiations over the last 12 months with the unions. Now, new lines are going in and they will be up and running by September or October.
"The company are saying that they are doing their bit to keep the site open and the union is working damned hard to reduce the impact of the change but we have got to be competitive against the other factories.
"There are a lot of people who do not like working here any more who want to get out. Sections of the workforce of a certain age do feel like that – they feel they are being put in a vulnerable position."
A spokesperson for Mondelez International said: "Change can be unsettling for anyone and we fully understand that as we start to roll out our £75 million investment into Bournville. That's why, as a responsible company, we have provided full support for everyone affected.
"Ultimately, whichever part of the business you work in, we all share a common goal to secure a modern, flexible and competitive future for Bournville and to ensure chocolate manufacturing continues here for the next generation."