DUP MP Sammy Wilson's office has been targeted with graffiti.
The word "traitors" was sprayed across the shutters of the East Antim MP's constituency office on Main Street in Larne.
It is the latest political party office to be daubed with graffiti in recent weeks.
Graffiti and posters have appeared in parts of Northern Ireland in opposition to post-Brexit Irish Sea border checks under the NI Protocol.
Alliance Party councillor Danny Donnelly condemned the latest graffiti incident.
Posting an image on Twitter, he said: "I'm very sorry to see DUP MP Sammy Wilson's office being vandalised in this manner.
"We may not always agree but this is no way to treat a democratically elected public representative."
Police said they received on Sunday a report of criminal damage, which is believed to have happened sometime between 4pm last Friday and 3pm on Saturday.
They appealed for anyone with information to phone 101 quoting reference 530 of 07/03/21, or Crimestoppers anonymously on 0800 555 111.
A report can also be made online via http://www.psni.police.uk/makeareport/ or http://crimestoppers-uk.org/.
It comes after constituency offices of DUP and Alliance representatives were targeted with graffiti some weeks ago.
Chief Constable Simon Byrne last week said there have been 200 incidents since January related to opposition to the protocol, including criminal damage, graffiti and the erection of posters and banners.
Unionists have reacted angrily to the post-Brexit arrangement, which they see as creating a border between Northern Ireland and the rest of the UK.
The DUP and other unionists have called for the scrapping of the protocol, which is aimed at maintaining an open land border with the Irish Republic.
