In a statement today the Bombardier's Northern Ireland management said it strong disagreed with the allegations made by Boeing.
It said the principal contractors will be Boeing Co., Northrop Grumman Corp., Raytheon Co. and General Electric Co.
Jerry Dias, president of Unifor, Canada's largest private-sector union, met Boeing officials in Washington on Tuesday to urge them to drop the case against Bombardier.
"The threat facing us, as a result of the ongoing case, is alarming and goes much wider than it may immediately appear".
In 2016, Canadian firm Bombardier won an order to supply up to 125 C-Series passenger jets to U.S. airline Delta.
May is expected to discuss Boeing and other issues with Canadian Prime Minister Justin Trudeau during a visit to Ottawa on September 18, a Canadian government official said, speaking on condition they not be identified since a formal announcement has not been made.
New details are emerging about the high-level, backroom wrangling around Boeing Co.'s dispute with Bombardier, which is quickly becoming an worldwide dog fight.
The federal government no longer talks directly to Boeing about the Super Hornet acquisition over the dispute, but, under the process known as a "foreign military sale", the Canadian government is officially a client of the U.S. government in this ongoing acquisition.
Liberal Party Senator Colin Kenny described the complaint as freakish.
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"Boeing is a big boy - it can take care of its interests by building a better plane at a lesser cost, I don't see why they're turning to their government now".
Boeing filed a petition with the US International Trade Commission and the US Department of Commerce in April, alleging that massive subsidies from the Canadian government have allowed Bombardier to embark "on an aggressive campaign to dump its CSeries aircraft in the United States".
A spokesman for the Department for Business, Energy and Industrial Strategy said: 'This is a commercial matter but the United Kingdom government is working tirelessly to safeguard Bombardier's operations and its highly skilled workers in Belfast.
May had a phone call with Trump last week in which she pleaded with the President to intervene in a legal battle between two rival aircraft manufacturers which threatens to destroy thousands of jobs in Northern Ireland.
The company said it is seeking "to restore a level playing field in the U.S. single-aisle airplane market". It has also complained about a £113 million loan ($150 million) from the British government.
Canada has threatened to retaliate by cancelling a lucrative order with Boeing for 18 Super Hornet fighter jets.
"Boeing had to take action as subsidized competition has hurt us now and will continue to hurt us for years to come, and we could not stand by given this clear case of illegal dumping", a spokesman for Boeing told the Times.
'We will continue our efforts to secure a resolution'.