Northern Ireland has temporarily suspended some checks at their border with the Republic of Ireland, and withdrawn staff from two ports over what one local council dubbed as "sinister and menacing behavior".
The border checks were implemented because of Brexit.
A local council made the move over concerns for staff safety, and police have said they now plan to increase patrols at points of entry.
The council whose staff inspected goods at Larne Port said graffiti describing employees as "targets" had appeared at the port.
The unionist mayor of a Northern Irish district has also said that he received intelligence that people had been recording the car registration numbers of port staff.
Many pro-British unionists fiercely oppose the new trade barriers introduced between Northern Ireland and the rest of the United Kingdom as part of the Northern Ireland protocol: a standalone deal for the region after Britain left the EU.
It was designed to maintain the principles of the Good Friday Agreement and Northern Ireland's open border with Ireland, and means that Northern Ireland will remain in the UK's customs territory - but will also be aligned with the EU's single market.
The EU commission said on Tuesday (February 2) that its staff will also be temporarily withdrawn from their work at Northern Irish ports.
A senior unionist, whose party has been calling on London to seek to remove the new trade barriers, has called for calm.
Partly blaming the EU for acting, quote, "crassly" to try and prevent vaccine exports through the Irish border.