The PSNI has warned DUP politicians with offices near Larne port their premises could be targeted by loyalists angry over the Irish Sea border.
Several party premises in the East Antrim and South Antrim constituencies have been visited in recent weeks, with staff warned to take extra precautions.
The police were not delivering targeted threats, merely offering advice. However, DUP politicians are understood to be taking the messages extremely seriously.
A party spokesman said: "The police should have no need to give security advice to those working in constituency offices. There is no place for violence, or threats of violence, in a democracy."
The warning came on the back of the party's East Antrim MP Sammy Wilson predicting that Brexit check problems at ports would get worse.
There have been a series of issues with the movement of goods between Great Britain and Northern Ireland, including a resolved row over Covid vaccines.
Mr Wilson said: "If you think it's bad at the minute, what's it going to be like in April once there's full implementation?"
It comes at a time of turmoil over the Northern Ireland Protocol element of the Brexit agreement, with rising anger among loyalists, who have been blamed for making threats against border control post (BCP) staff in Larne.
Customs checks were temporarily suspended last week at Larne and Belfast ports, with a dozen employees withdrawn from the Larne BCP after sinister graffiti appeared warning "all staff are targets".
They resumed work on a phased basis last Wednesday after a security risk assessment by Stormont officials was carried out at all three BCPs, including Belfast and Warrenpoint, as well as "a full threat assessment from the PSNI".
Loyalist signs pictured in Dungannon, Co Tyrone, yesterday warned "No border in the sea or we continue the fight".
Sammy Wilson said: "I can totally understand why people are angry. I also understand why they lash out.
"I have no doubt that they saw the threats of violence were rewarded with the protocol, so people who are minded to engage in violence will say 'That seems to be the answer to the problem - just threaten violence and sure you'll get whatever you want'.
"I think they're wrong in doing so. There's no point in putting pressure on environmental health officers just doing their job that they are employed to do and are not in any way involved in the politics of this. So I can sympathise with those people who now find themselves in the front line of what is basically a political problem cynically created by people like Boris Johnson, who were more interested in ensuring the unity of the Conservative Party and winning a general election.
"The real culprits in all of this are not the poor people who work at the front line. The real culprits are the cynical politicians in Northern Ireland and the Republic who created a problem which wasn't a problem on the frontier between Northern Ireland and the Irish Republic. And don't forget this is before the full implementation of this agreement. This is during the grace period, when we're given certain freedoms not to have some things checked and not have checks as rigorous as what they will eventually be."
Fuel was added to the fire last week by Loyalist Communities Council chairman David Campbell saying it may be necessary to "fight physically to maintain our freedoms within the UK".
Alliance Party leader Naomi Long said "the EU was good for Northern Ireland, playing a vital role in its peace and prosperity".
The Justice Minister added: "Because the unionist parties, especially the DUP, turned down more moderate ways to manage Brexit - including even arguing against a longer transition period to allow businesses greater time to prepare - and pursued a harder version, we are now dealing with those consequences, namely the Northern Ireland Protocol.
"We have been working with the Government and EU to bring as many mitigations and flexibilities as possible. In the meantime, the undeliverable promise of a 'perfect' Brexit from some quarters, the ignoring of facts, the scapegoating of some and the ratcheting up of rhetoric has helped fuel increasing tension here."