Nearly 300 job could be lost after two Derbyshire employers confirmed they were looking at restructuring.
About 170 posts may go at the Airfoil Technologies International factory in Codnor, Ripley, after the firm said they were looking to close the site.
Bosses said they had been affected by the downturn in the aviation industry.
At the same time around 100 positions are threatened at Celanese chemicals in Spondon. Managers said they might have to shed a fifth of the workforce.
A statement from Airfoil Technologies International said they deeply regretted having to take this course of action and were in talks with the workforce, with a view to finding alternative posts in the business.
Celanese HR manager, Halinka Hepworth, said they needed to keep the business competitive but total numbers are not yet set in stone: "At the moment we have said around 100.
"But to be honest it is a very difficult number to define at the moment because we are in a 90 day consultation period and we need to look at the detail of that and talk to the employees with regard to where we are looking to make those reductions."