Political calls were made for "cool heads" and "calming language" after border checks at Larne and Belfast ports in Northern Ireland were suspended amid concerns for staff safety.
Politicians from both sides of the border appearing before the Seanad Special Select Committee on the Withdrawal of the UK from the EU condemned the threats made to border inspectors.
Colin McGrath, SDLP MLA for South Down and chairman of the Stormont Executive Office Committee in the Northern Ireland Assembly, said the threats were "absolutely deplorable, "sinister and unwarranted", and had to be "condemned roundly by all politicians of all shades".
“We do need cool heads, calming language,” he said.
Mr McGrath urged Northern Irish politicians to be "very careful" about their comments around Brexit and the Northern Ireland protocol opposed by Unionists politicians.
“A communication or miscommunication from a politician could be considered as a heads up for people to carry out certain behaviours within the community,” he said.
He told the committee that politicians can “take the heat out” of the situation by informing people about the facts around Brexit and taking political identity out of the debate and ensuring no void is left to be filled by “social media armchair commentators” spreading misinformation.
The border problems were not down to the Northern Ireland protocol but Brexit, and there would be “significant teething problems” from the UK leaving “a major institution”, he said.
Sinn Féin MLA for Foyle Martina Anderson told the Seanad committee that people need to be sued if threats were being made on social media and people arrested if number-plates of border inspectors were being checked. She said unionists “must call on people to stop making threats”.
She noted that there did not seem to be a threat from loyalists and that the Police Service of Northern Ireland had not confirmed that these threats were coming from loyalists.
Mr McGrath urged those making the threats to recognise that those officials were working to make the Irish Sea trade border “easier and more seamless”.
He accepted that trade with Britain was being affected but he believed these difficulties would be temporary and needed to be made “as simple as possible” and “steamlined”.
“The border is still down the Irish Sea in terms of trade, but there is nobody that is going to be able to fix because they have threatened them and they have had to be taken out,” he said.
“So I would ask those that have issued the threats to actually take a step back, maybe think: is what they have done actually counterproductive?”
Senator Michael McDowell said he hoped the difficulties with paperwork and checks that have affected supermarket supplies in Northern Ireland could be “reduced to an absolute minimum” as these could “seep into a widening of support for the boycott of customs inspections”.
Fianna Fáil senator Lisa Chambers, the committee's chair, said that the committee's senators "utterly condemn the intimidation of staff at the ports".
She expressed concern that if problems remained with trade between the North and Britain and these tensions continued, there would be “difficulties” in four years when the Northern Ireland Assembly votes whether to maintain the protocol under the terms of the Brexit treaty.
“There are tensions there. They are bubbling away,” she said.