Up to 600 government jobs could be relocated following the announcement that the Office for National Statistics (ONS) will close its London office in three years time.
The ONS, the executive agency responsible for collating official economical and demographic data, plans to close its office at Drummond Gate, Pimlico, south London, by 2010 and relocate staff to Newport.
But the Public and Commercial Services union (PCS) says that 200 people could be made redundant.
Under the plans, the London office's staff numbers will be reduced by 240 over the next year, with only 50 workers remaining by 2010.
While the majority will move to the ONS' headquarters in Newport, some will relocate to Titchfield, the organisation's demographic centre.
A spokesperson said that the changes would "reaffirm" Newport as the ONS' corporate headquarters, a status it assumed from Drummond Gate in 2005.
According to the representative the relocation will not only reduce accommodation costs but also "promote closer working relationships and reduce risks associated with working from split sites".
But Mark Serwotka, general secretary of the PCS, has vowed to fight the planned relocation.
"These plans are unnecessary, ill thought out, and will undermine the quality of the statistics that the government base new initiatives and policies on," he said.
"With compulsory redundancies likely on a far larger scale than ever before, today's announcement will anger staff, stiffen their resolve and increase the likelihood of a civil service wide strike. If the government are to avoid a conflict with its own workforce then it needs to move swiftly in giving assurances over jobs and services."