The world's No. 1 fiber-optic cable company, Corning (GLW) - Get Report, was down 6.9% in preopen Instinet trading after saying Wednesday evening it was expanding its restructuring efforts and lowering estimates for the third quarter.

Corning said deteriorating economic conditions in all its businesses, particularly in sales of fiber optics to telcos, have forced it to cut 4,000 more jobs and temporarily close plants, resulting in charges of up to $1 billion in the second half of 2001.

The company said earnings will be 2 to 6 cents a share, below analysts' estimates of 12 cents. It also expects to report a fourth-quarter pro forma net loss, compared with a profit of 9 cents expected by analysts.