Around 2,500 civilian Ministry of Defence (MoD) workers are being balloted on industrial action over job losses and relocation. Union leaders want staff at the MoD's Defence Logistics Organisation (DLO) to support a work to rule.
The MoD plans to concentrate jobs in Bath and Bristol.
The proposals affect staff at Andover, Hants; Caversfield, Oxon; Wyton, Cambs; Telford, Shropshire; and Sherborne and Yeovilton in Somerset.
 | The MoD stands ready to take part in constructive dialogue |
The MoD wants to merge its Defence Procurement Agency and Defence Logistics Organisation, but at this stage only union members in the DLO are being balloted.
The Public and Commercial Services Union told BBC News that, if approved, it wants a work to rule to begin shortly after the ballot ends on 22 September, adding that strike action has not been ruled out.
In a statement, the MoD said: "This co-location will save around �200m over 25 years, money that can be reinvested in the front line.
"We are aware that the union is balloting its members today, as is their right.
"The MoD stands ready to take part in constructive dialogue, as we have been since 3 July."