Industrial action at the NI Electoral Office in Banbridge and other areas will disrupt preparation for the EU referendum,a top union has warned.
Strike action has been scheduled for Friday, 3 June and Tuesday, 7 June.
These dates are the deadlines for postal vote applications and voter registration.
Public service union Nipsa added that further strike action could be scheduled “up to and possibly including the day of the referendum”.
The referendum vote will be held on Thursday, 23 June.
Union members had voted to take industrial action over plans to close six regional electoral offices.
The offices facing closure are in Banbridge, Ballymena, Londonderry, Newtownabbey, Newtownards and Omagh.
The Electoral Office plans to centralise many of its services in Belfast.
The Electoral Commission has said it is focused on “ensuring that voters don’t face disruption.”