Tyre manufacturer Michelin is to close its final-salary pension scheme to existing members in the UK and transfer staff to a money-purchase plan.
The French company said it was making the move to tackle a continued deficit of more than £250m, despite pumping £100m into the fund.
The Transport and General Workers Union (T&G) said it was “dismayed” at the decision, saying it would throw retirement plans for 4,200 staff into chaos.
The closure will also affect staff employed by the ATS chain of tyrefitters.
The new scheme is set to be launched in 18 months’ following a consultation period, Michelin said.
Rob Taylor, T&G convenor at the Stoke-on-Trent plant, said: “This looks like a fait accompli by Michelin, which throws the retirement plans of more than 3,000 people into chaos.
“We will go into the consultation with our eyes open and we’ll call for meaningful talks and serious consideration of alternatives to closure, but our fear is the company has made its mind up.”