The union Unite has said that DUP MPs must use their power at Westminister to put pressure on the Prime Minister to do everything she can to protect jobs at Bombardier.
The union made the call as yet more crippling US import tariffs have been imposed on Bombardier's C Series aircraft, in its trade row with Boeing.
The extra costs could threaten jobs in Belfast.
A ruling by the US Department of Commerce on Friday has quadrupled the cost of the aircraft being brought into America.
It has hit Bombardier with an 80% import tariff.
That's on top of another 220% tariff imposed less than two weeks ago.
Despite appeals from Theresa May to President Trump on the matter, Unite the Union says the Prime Minister isn't doing enough.
UTV's business reporter Vicki Hawthorne reports.