Cleveland Bridge, a 144-year-old company that has produced and designed some of the iconic steel structures has called in administrators – leaving 200 staff uncertain of their future.
The company, whose plant is in Darlington and Sedgefield constituencies seized by the Conservatives from Labour in December 2019, said it was "actively taking advice and exploring a range of options".
Shadow Business Minister Seema Malhotra said: "This is extremely worrying news and my immediate thoughts are with every affected employee who may be feeling anxious about their livelihood.
“The Government must explain as a matter of urgency what it is doing to protect these jobs, and ministers must also dig deeper and explain how it can be possible that an engineering company of this significance – a major employer in the North responsible for building landmarks across our country – can be in such a perilous position.
“This news underlines again that we need a long-term plan for our steel industry which is vital for our economy and national security.
“The UK has a proud manufacturing history and it's crucial government backs Britain's manufacturers to secure their proud future."
Darlington MP Peter Gibson was hopeful a buyer could be found.
“The fact it has got an 18-month pipeline of work is a very positive sign and the heritage is truly fantastic.”
The news came hours after the third meeting of the UK Steel Council, chaired by Business Secretary Kwasi Kwarteng and which includes industry chiefs, unions and ministers.
Earlier this week, Mr Kwarteng suggested ministers were ready to back an overhaul of the sector to make it more environmentally-friendly.