Alison Jones, Unite regional office, said that if the transfer does go ahead, it would potentially lead to the redundancies of the majority of the staff.
She said: "Following on from the initial announcement by Transactis on 13 January, there has been a great deal of concern surrounding the proposed transfer of various departments to RR Donnelley.
"We received confirmation on Friday that the measures connected to the transfer would indeed lead to wide-scale redundancies from the highly skilled, loyal and dedicated workforce, which is devastating news.
"The employees at Transactis, through their hard work and commitment, have helped the company to win valuable contracts which, ironically, should have secured their future."
Jones added that with the current economic and jobs climate and the fact that Transactis is a major employer in the area, staff are understandably extremely concerned by the proposal.
"Unite and [fellow union] USDAW are now in a consultation period regarding the proposed transfer and will work together to ensure that everything possible is being done to represent the interests of their members."
The next consultation meeting will be on Friday (28 January) and Jones said that Unite was negotiating for transfer rather than redundancy.
Richard Higginbotham, head of marketing at Transactis, said: "I can confirm that consultation meetings about the TUPE process took place on Friday with representatives from trade unions and representatives from our Document Services, Reprographics and Procurement teams – our Data business is not part of this process and is unaffected.
"I am not able to comment on RR Donnelley's plans. Everything discussed is still subject to consultation and we will continue to communicate with and support the individuals affected throughout this process."
Last week, Transactis said it intended to accept an offer from RR Donnelley to purchase its document services, reprographics and procurement operations. RR Donnelley declined to comment.