Nov. 5 (Bloomberg) -- CVS Caremark Corp., the largest U.S. provider of prescription drugs, said the Federal Trade Commission is probing some its business practices.

CVS is confident it conducts business in compliance with antitrust laws, Chief Financial Officer David Rickard said today in an e-mailed statement. CVS was notified of the investigation in August and is cooperating, the Woonsocket, Rhode Island-based company said today in a regulatory filing.

The FTC is investigating certain CVS business practices, Peter Kaplan, a spokesman for the Washington-based agency, said in a telephone interview. He wouldn’t discuss which practices are the target of the probe.

CVS, which operates more than 7,000 drugstores, entered the pharmacy-benefits management business in 2007 with the purchase of Caremark Rx Inc. for about $22 billion. Members of Congress have asked the FTC to investigate whether the combination hurt consumers after similar concerns were raised by Change to Win, a 6 million-member union federation.

Change to Win said in September that it met with FTC Chairman Jon Leibowitz. The group alleges that CVS overcharges consumers, sells private customer data and favors higher-priced drugs in order to collect manufacturer rebates. CVS denies those assertions.

The company fills or manages more than 1 billion prescriptions a year through its retail stores, mail-order business and the Caremark pharmacy benefits manager.

CVS posted its biggest drop in eight years in New York trading today after saying the pharmacy-benefits management unit lost $3.7 billion in contracts in the third quarter and forecasting narrower margins next year.

The shares plunged $7.28, or 20 percent, to $28.87 at 4:15 p.m. in New York Stock Exchange composite trading, the biggest one-day decline since 2001.

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Last Updated: November 5, 2009 16:23 EST