Port workers could become very anxious over threatening loyalist behaviour, a senior trade unionist said.

Inspections at Larne and Belfast ports were suspended on Monday after sinister graffiti and reports of intelligence-gathering on officials carrying out post-Brexit checks.

Recently police warned of growing discontent over the Northern Ireland Protocol, which keeps the country following the EU’s trade rules and has created significant extra paperwork, but said their feedback was not causing significant concern.

Patrick Mulholland, deputy general secretary at the NIPSA union, represents some of the workers at the ports.

We do not want to see our members becoming a political football around the issue of the border, be it a land or a sea border

He said: “They, first of all, tend to be in shock because they suddenly find themselves under a level of threat they would not expect to be under.

“These are ordinary working people.

“They then become very anxious because they do not know how this is going to work out and they do want the greatest possible level of support and assurance from their fellow workers and people in society that they have got their backs.

“That is very important.”

He said he wanted to ensure the safety of his members.

“We want to ensure that they are not under any threat and that they are able to go about their work as they would normally be able to go about their work and we want to make sure that they are treated properly by their employers.

“We do not want to see our members becoming a political football around the issue of the border, be it a land or a sea border.”

He added: “One of the strongest traditions of the trade union movement is that when workers are under attack and under threat, the whole of the trade union movement stands shoulder to shoulder and sends a clear signal that this is not acceptable and that we will do what we need to do to defend our members’ rights and their safety.”

Public and Commercial Services union general secretary Mark Serwotka said it was an outrage that members doing critical work at the border in Northern Ireland are being subject to death threats and intimidation.

Sectarian violence has no place in Northern Ireland and we are calling on employers and the police to work closely together to ensure port and border staff safety

The union represents customs port and border force staff in Northern Ireland.

He said: “Sectarian violence has no place in Northern Ireland and we are calling on employers and the police to work closely together to ensure port and border staff safety.”

Irish Congress of Trade Unions assistant general secretary Owen Reidy called for the threats to be lifted.

He said since the UK left the EU last month, there has been a litany of over-the-top commentary about an Irish Sea border, adding to an atmosphere of fear among people susceptible to “hype” about an economic United Ireland.

“What is happening with the Northern Ireland Protocol is very far from that assertion,” he said.

“The Northern Ireland Protocol was backed reluctantly by the trade unions across Northern Ireland as the least-worst option and we believe that the structures we have must be seen to operate, otherwise whoever was behind these threats to workers will be rewarded.

“Trade unions need the rule of law to help protect workers and their right to carry out their duties safely.”