Aerospace firm Bombardier is planning to cut another 280 jobs at its Northern Ireland operations.
It is the latest in a series of redundancies which form part of the company's five-year plan to cut costs and increase profitability.
Meanwhile, the oil field services firm, Schlumberger, is proposing to close its Newtownabbey plant next year putting more than 200 jobs at risk.
It said the industry was enduring the worst "downturn of the past 30 years".
Last year, Bombardier cut 1,000 jobs in NI - about 20% of its local workforce.
In September it said a further 95 support staff would be made redundant.
Analysis: John Campbell, BBC News NI economics & business editor
It has been a gloomy week for manufacturing: Production ceased at JTI in Ballymena, Bombardier is making more redundancies and Schlumberger's plant faces closure.
But the full picture is more complicated.
The latest quarterly employment survey for the quarter to June 2017 showed the sector is still adding jobs, albeit at a marginal rate.
The number of manufacturing employees was up 1.1% over the year to 82, 970.
On a longer view of the recovery, from June 2012 to June 2017, manufacturing jobs increased by 11%, making it the best performing sector.
It may be that the next survey will show employment falling as previously announced redundancies feed through.
But manufacturing still remains an important part of the Northern Ireland economy.
In a statement, Bombardier said: "We continue to review our manpower requirements in Belfast and regret to confirm that we must reduce our workforce levels by around 280".
"Those impacted will be functional support personnel, including managers and professional staff."
The company has faced severe financial pressure as cost overruns on its new C-Series jet drained cash out of the company.
That pressure was eased last week when Airbus said it would take a majority stake in C-Series project with a view to buying it outright.
Davy Thompson of Unite described the Bombardier job losses as devastating and "premature".
"This news is all the more concerning as it comes despite management pronouncement that the Airbus acquisition of a 50.01% stake in the C-Series programme might result in a potential doubling of production on site," he said.
"Unite has highlighted the fact that Airbus paid nothing for this stake and that it will only come into effect in the second half of 2018.
"It means that the deal, while providing some hope for the C-Series in the future, has made little to no impact on the financial pressures faced by the company in the present."
Newtownabbey job losses
Schlumberger said it currently employs 205 full-time people, including contractors in Northern Ireland.
However, it said the oil and gas industry is going through "the most severe downturn of the past 30 years with operators significantly reducing their investment".
The company said it understands the impact of its announcement and the impact the proposal to close its Newtownabbey plant would have if it goes ahead.
Schlumberger said: "Every effort will be made to support our employees, including potentially transferring some staff to other locations.
"We will continue to identify opportunities such as this, as they become available."
Susan Fitzgerald from Unite described the news as "another hammer blow for Northern Ireland's manufacturing sector".
"We are aware that they have transferred much activity formerly conducted onsite at Newtownabbey to other, low-cost locations, including China," Ms Fitzgerald said.
"We are concerned that the company's global corporate management are attempting to use the downturn in the oil and gas sector as cover to further outsource jobs to low cost alternative locations. If so we will be rejecting their logic."