Mr Cunningham said: “The company has made it clear it’s a very old plant, it’s outdated and needs huge investment in order to bring it up to modern standards.
“They’re talking about hundreds of millions of pounds and say the plant doesn’t make that much.
“A week before Christmas, it must be devastating for the workers. They’ve got tremendous skills.
“The chief executive is one of the richest people in the world, but he prefers to invest his money in the Middle East rather than Teesside.”
‘Decades of underinvestment’
In the email sent to Mr Cunningham, Ineos said it had “reluctantly concluded that the plant should close”, citing safety concerns for its employees handling “significant quantities of hazardous material”.
The firm said it had invested almost €200m (£178m) in the site since it purchased it in 2008, but added it would require another €200m “to try to counter decades of underinvestment”.
Staff would be supported through the firm’s employee assistance scheme, it said, with the possibility some could transfer to other factories.
A second plant on the 268-acre site, which produces industrial nylon, will remain open. It is operated by Ineos on behalf of Basf.