Dow Chemical Co said it will post a fourth-quarter charge of as much as $1.1 billion related to last week's announcement that it will close 20 plants and lay off thousands of workers.

The largest U.S. chemical maker said the restructuring program -- its second of 2012 -- was necessary due to dropping demand for its plastics and other products.

Dow will record a charge of $900 million to $1.1 billion for the layoffs, plant closures, as well as the write-down of Dow-Kokam LLC, Dow's lithium ion battery joint venture. The disclosure came as part of a filing with the U.S. Securities and Exchange Commission.

The Midland, Michigan-based company will lay off 3,000 workers in total, but the net job loss will be roughly 2,400 as the company plans to boost staff in growth areas.

Shares of Dow have dropped 15 percent in the past six months.

(Reporting By Ernest Scheyder)