New York City ? AT&T Inc. will take a $1 billion noncash accounting charge in the first quarter because of the health care overhaul and may cut benefits it offers to current and retired workers.

The charge is the largest disclosed so far. Earlier this week, AK Steel Corp., Caterpillar Inc., Deere & Co. and Valero Energy announced similar accounting charges, saying the health care law that President Barack Obama signed Tuesday will raise their expenses. On Friday, 3M Co. said it will also take a charge of $85 million to $90 million.

White House spokesman Robert Gibbs said Thursday that the tax law closed a loophole.

Under the 2003 Medicare prescription drug program, companies that provide prescription drug benefits for retirees have been able to receive subsidies covering 28 percent of eligible costs. But they could deduct the entire amount they spent on these drug benefits — including the subsidies — from their taxable income.