The Transport and General Workers Union claims that gas company BOC is to close its final salary pension scheme to new entrants.
The union reports internal consultations are taking place at the firm over closing entry to the scheme.
Jimmy Elsby, T&G assistant general secretary, who heads up the union's manufacturing taskforce, said: "Once again we see a blue chip British company trying to sort out its problems by transferring the risks of future pensions provision to its workers. The two-tier pension is being considered again.
"We have had a good relationship with BOC over the years and are surprised at this decision. As a consequence, the union will be seeking an urgent meeting to discuss the exact nature and scope of this internal review.
"Our starting point will be that everything should be done to avoid closure of the scheme to new entrants."