It will take a $1 billion charge against earnings because the federal healthcare overhaul cancels a tax benefit the company received, says AT&T Inc.

AT&T, and other U. S. companies that provide prescription-drug benefits to retirees, receive a federal subsidy, the value of which also can be deducted from the firms' taxes.

The Wall Street Journal reported on Saturday that the healthcare overhaul plan signed by President Obama this week cancels the deductibility of the subsidy.

Roland McDevitt, head of healthcare research at Towers Watson, a benefits consultant, said that they "have a stream of tax benefits that they are losing way out into the future."

The Journal also reported that so far, other companies taking the one-time charge include 3M Co., Deere & Co., Caterpillar Inc. and AK Steel Holding Corp.

It was further estimated by Credit Suisse this week that companies in the S&P 500 index combined could take as much as a $4.5 billion charge due to the change in the value of the tax asset. (With Inputs from Agencies)