Birmingham Chamber of Commerce boss Jerry Blackett is on a collision course with unions over the future of thousands of Cadbury jobs under global giants Kraft.

Concerned union leaders have thrown down the gauntlet to Kraft boss Irene Rosenfeld over an alleged “hardening of attitudes” towards Cadbury workers and “less willingness to consult”.

Potential battle lines are being drawn between the union Unite and the US confectionery firm just over a year after the controversial £11.7 billion takeover was approved.

But Birmingham Chamber chief executive Mr Blackett has opposed the unions by publicly questioning the stance of MPs who challenged Kraft bosses on its reluctance to guarantee jobs beyond two years.

In a letter to the Birmingham Post, Mr Blackett said: “I question how MPs who challenged Kraft Foods at the business select committee can demand the company to guarantee jobs indefinitely.

“Manufacturing businesses across the country, large and small, need to become more productive to compete in a competitive global market during tough economic times.

“To require any manufacturer to give a cast-iron guarantee on jobs in this enivironment is unreasonable and counterproductive. I can’t think of any business in the West Midlands, no matter how successful, that would want to do this.

“Kraft Foods and Cadbury had a successful 2010. The company is honouring its two-year promise on jobs, which still has a further year to run, and is investing in Bournville and its other UK factories.

"The company has created new highly-skilled jobs by making Bournville its global centre for chocolate R&D.

"The fact that Kraft Foods is investing in Cadbury in the UK should be commended, not lambasted.”

Ms Formby sent a letter of concern to Ms Rosenfeld after Kraft managers told MPs at a Commons business select committee hearing they were conducting a “harmonisation project” bringing Cadbury workers’ terms and conditions into line with the US group.

Unite’s national officer for food and drink Jennie Formby said: “Our stewards have reported a perception that there is a general hardening of attitudes and less willingness to consult.

“We do not want our relationship to be strained – we want a positive relationship with employers but it seems that they do not want that kind of relationship.

“Changes are being brought in without consultation – in the past Cadbury management always consulted with the unions.”

Ms Formby’s letter to Ms Rosenfeld says: “I note with surprise and concern that your executives who attended the BIS select committee in London announced that Kraft has an intention of harmonising terms and conditions of employment of the acquired workforce, presumably with those currently working for Kraft.

"As the national officer with responsibility for our members in former Cadbury sites I would expect to have direct contact from your management on any issue relating to terms and conditions rather than learning about it via the press.

“I would therefore request that urgent contact is made to discuss this matter to enable Kraft to fulfil its legal obligation to consult in a meaningful manner.”

Ms Formby goes on to ask Ms Rosenfeld for details of Kraft’s business plan for manufacturing sites in the UK and Ireland for up to 10 years.