Brazilian aero firm Embraer says it is not interested in "killing" Bombardier, but wants it to behave like a "normal commercial enterprise".
The World Trade Organisation opened a panel last week - the initial stage of dispute resolution - after Brazil complained earlier this year about alleged subsidies Canada has provided to Bombardier, which is Embraer's biggest rival in the global regional jet market.
Last week the US Department of Commerce delivered a preliminary ruling following a separate complaint made by Boeing against Bombardier.
The Canadian-owned firm employs more than 4,000 workers in Belfast.
Boeing claimed that the Canadian company had been able to sell dozens of its C Series jets to US airline Delta at below cost because it had received subsidies.
Bombardier denied the claim, but has been hit with a 220% levy on sales of C Series jets into the US.
The ruling has caused a political and commercial rupture between Canada and the US, as well as between the UK and US.
About 1,000 of the Northern Ireland jobs are directly involved in making wings for the C Series jets.
Embraer Commercial Aviation chief executive John Slattery said: "I don't want to sink anybody.
"There's room for everybody. I've no interest in killing Bombardier.
"It's not in our DNA. All we want is a level playing field, where they behave like a normal commercial enterprise."
He added: "As an Irishman, I paid attention to what was being said about the jobs in Belfast. But we're not trying to put anyone out of business.
"If they can keep going back to their government for equity or for loans, when the rest of the commercial market is closed to them for equity or debt, then that's unfair by anybody's sensible and sober calculus."