A potential 25% tariff to be imposed on steel imports to Northern Ireland not from Great Britain will ruin the industry, it has been warned.
SDLP MLA Colin McGrath said he has written to the Chancellor, Rishi Sunak, on the issue.
The Belfast Telegraph reported yesterday how the steel sector here had been left confused and uncertain by the unexpected tariff.
At least one trader was charged the 25% on product that had been cleared in the Republic of Ireland, while others have imported steel here without realising they face the extra cost, according to one leading market analyst.
The Brexit Protocol means that Northern Ireland is treated as if it were part of the EU's single market.
It means any steel imported from exporters around the world will, in theory, be hit by a 25% tariff.
The protocol terms also mean that any exports from Britain to here will count as part of the UK's quota - and could lead to the quota being used up more quickly. Once it is exceeded, then tariffs of 25% would apply on British steel entering Northern Ireland.
A briefing note by the UK steel lobby, obtained by RTE News, states: "The special status of NI complicates matters further, as steel exports from GB to NI are considered 'at risk' of moving into the EU/ROI.
"As a result, most steel exported from GB to NI is effectively treated as an export to the EU and therefore will be subject to the EU's Steel Safeguarding measures [ie, tariffs]."
Mr McGrath, a South Down MLA, said he was shocked by the tariff.
"Let's be under absolutely no allusion - this decision by the UK Government has the potential to decimate the steel industry in the north," he said.
Mr McGrath accused the Conservative government of "trying to bleed these businesses' already depleted finances completely dry".
He added: "I have already written to Rishi Sunak MP and called upon him to answer why the duty was imposed, why it was imposed without warning and without consultation with businesses here, and I am calling for it to be scrapped."
Stephen Kelly, chief executive of Manufacturing NI, told RTE: "In a very short period of time, unless we can get those stocks of steel returning and unless we can get that rest of the world stuff, then we have the potential to be shutting dozens and dozens of factories because we just won't have the supply of steel."