Aircraft maker Boeing has become a scapegoat for Bombardier job cuts in Belfast, the firm said.
Criticism of the aerospace giant over its trade dispute is a "smokescreen" to disguise its Canadian rival's problems, senior management claimed.
The number employed by Bombardier at manufacturing plants in the north has fallen considerably over recent years, Boeing told a committee of MPs.
Thousands of Belfast posts could be threatened if a proposed 300% duty on exports to the US is imposed on Bombardier's new C-Series jet following a complaint by their competitor. The wings are made in Northern Ireland.
Sir Michael Arthur, president of Boeing Europe and former British ambassador to Germany and high commissioner to India, said: "The reason those jobs are at risk is because of the management of Bombardier taking certain decisions that put those jobs at risk.
"Boeing is being used as a scapegoat for that reduction in Northern Ireland jobs which we all regret but which in a way pre-dates the issues."
The Northern Ireland Affairs Committee of MPs at Westminster is investigating steps taken to protect jobs in Northern Ireland.
Atlanta-based Delta Airlines has placed a major order for C-Series planes and many Belfast positions at Bombardier and throughout the supply chain hinge on that order being fulfilled.
Sir Michael reiterated Boeing's assertion that its legal action was about creating a level playing field between competitors bidding for sales.
Boeing has claimed Bombardier used state subsidies to "dump" their planes on the US market at below cost price, giving them an unfair advantage.
Critics of Boeing's legal action claimed the firm also received subsidies from the US administration in the form of defence spending and said its aircraft were not in direct competition with a version of the C-Series at the heart of the current dispute.
Sir Michael said: "This was a pure commercial challenge for a sale that we felt was unfair."
DUP MP Ian Paisley retorted: "It is spiteful, not commercial."
Committee chairman Andrew Murrison said Boeing could not satisfy demand for its planes. Its order book from airlines would take years to clear even though it was ramping up production to "historic" high levels.
Sir Michael said: "We were the victim of a dump sale which we had to challenge in the interests of a level playing field.
"We like competition, it makes us better, but we want it to be fair competition.
"We believe in the rule of law and trade law and compliance with that.
"It is very much a legal not a political process which is running forth in the US."
Another senior Boeing official said Bombardier's problems were "deep-rooted" and pre-dated the current dispute.
He told the committee: "It is effectively a smokescreen to blame Boeing for their problems."
Mr Paisley claimed the firm's reputation had been tarnished.
"This has been a public relations disaster," he said.
"The impact of this is reputational damage to your company from crushing the wee guy."
The North Antrim MP said it had turned into a very toxic political dispute, with issues being raised on Capitol Hill, the British prime minister ringing US President Trump and former defence secretary Sir Michael Fallon threatening jobs and potential sales in the UK in retaliation.
Sir Michael responded: "When we see illegal action would you expect us to ignore it?"
Earlier this year, in response to Boeing's complaint, the US Department of Commerce announced it would impose an interim tariff of nearly 220% on the jets.
A second preliminary levy of 80% had been loaded on sales of the Bombardier aircraft.
Assembly of the C-Series will be carried out at the Airbus factory in the US state of Alabama under a partnership which Airbus and Bombardier believe will mean it avoids import tariffs.
