Thousands of Bombardier workers in Northern Ireland will "flex their muscles" if a trade ruling goes against the aircraft manufacturer, a union leader has warned.
The United States Commerce Department has confirmed plans to impose duties of 292% on imports of Bombardier's C Series commercial jets.
Unite has called on the US International Trade Commission (ITC) to set aside the decision when it meets in the coming days to discuss whether rival Boeing has suffered injury or loss as a result of Delta Airlines' order of C Series jets.
Regional officer Susan Fitzgerald told a rally at Bombardier's East Belfast plant: "As workers we won't be collateral damage in a trade war. We demand political action at the eleventh hour.
"This is a dress rehearsal for the action we may need to take post the ITC decision.
"There is no harm today that we give a glimpse of the ferocity here of Bombardier workers united and mobilised in a common cause.
"There is no harm that everyone sees what it is like when a workforce with this size and power flexes their muscles."
Owen Reidy of the Irish Congress of Trade Unions said Bombardier workers may have to rely on the "collective power" of the trade union movement across Ireland.
"We will be asking for support and solidarity," the assistant general secretary said.
He the dispute represented a challenge and a threat for every worker in Northern Ireland.
Many Belfast positions at Bombardier and throughout the supply chain hinge on Delta's order being fulfilled.
Boeing has claimed Bombardier used state subsidies to "dump" their planes on the US market at below cost price, giving them an unfair advantage.
Trade unions estimate that a total of 24,000 jobs are at risk if tariffs are imposed.
Unite regional secretary Jackie Pollock said: "If these brutal tariffs are upheld there's no question that it represents a serious threat to the very existence of Bombardier in Northern Ireland."
The Government has said it is working tirelessly to secure the future of the C Series.
Mr Pollock said the Prime Minister's "huge effort" to defend jobs amounted to two phone calls to Donald Trump.
"Two phone calls is the sum total of what this Prime Minister can do for jobs," he said.
"With 24,000 jobs at risk, a community on the edge of ruin and a peace process which has failed to deliver - we are told two phone calls is all we are worth.
"Not good enough."