What's going on with Boeing and Bombardier?
Thousands of jobs are at risk at Bombardier, one of Northern Ireland's biggest employers, after the US Department of Congress imposed a 220% tariff on some of the aeroplane company's products following a dispute with Boeing, another international transport company.
What's the government said?
The PM has backed defence secretary Michael Fallon's remarks that Boeing's dispute with Bombardier could jeopardise future defence contracts with the UK, BuzzFeed News understands.
"Not the kind of behaviour we would expect from a long-term partner," Fallon said, "and it could jeopardise our future relationship with Boeing."
He added: "Boeing stand to gain a lot of British defence spending. They will also be bidding for other defence work and this kind of behaviour clearly could jeopardise our future relationship with Boeing."
What's the dispute really about?
Boeing complained that Bombardier got unfair subsidies from the UK and Canada. Bombardier responded by saying its products are "superior". The US tariff could cause Bombardier to pull out of Northern Ireland, risking at least 4,100 jobs.
The dispute centres around a particular kind of aircraft, the C-series, which Bombardier manufactures in a purpose-built £520 million factory in Belfast. Fifteen NI aerospace firms supply parts for the C-series. So if Bombardier goes, they're at risk too.
Do people think it's the government's fault?
Ross Murdoch, the GMB union's national officer, called the decision a "hammer blow" and warned that there could be further implications for British workers.
"Theresa May has been asleep at the wheel when she could and should have been fighting to protect these workers," he said. "It's high time she woke up."
Labour leader Jeremy Corbyn, speaking at his party's conference in Brighton, said if the special relationship between the US and UK meant "anything" then Britain needed to be able to state: "That way is the wrong way."
"That’s clearly what’s needed in the case of Bombardier where thousands of jobs are now at stake," he said. "A prime minister betting our economic future on a deregulated trade deal with the US might want to explain how 220% tariffs are going to boost our exports."
Meanwhile, Labour's shadow secretary of state for Northern Ireland Owen Smith hammered the PM over her failure to protect British interests.
“This damaging ruling was widely predicted and yet our government appears to have done very little of substance to persuade either Boeing to withdraw its claim or the US Administration to rule against it," he said in a statement.
Smith said he had written to May "a fortnight ago", urging her speak out to protect workers – "as vigorously as her Canadian counterpart has done" ahead of the decision.
Doesn't this have big implications for the future what with Brexit and all?
You might very well think that. Some pointed out the apparent closeness of May and US president Donald Trump, and the government's assurances that trade with the US would mitigate many of Brexit's losses.
Pro-Remain MPs are saying this shows May can't rely on Trump in future.
However, a spokesperson for the Department for Business, Energy, and Industrial Strategy emphasised that the decision was "only the first step in the process".