WASHINGTON – A group of state lawmakers is asking federal regulators to investigate whether the 2007 merger that created pharmaceutical giant CVS Caremark Corp. has led to higher prescription drug prices for Americans.

In March 2007, Woonsocket-based CVS Corp. bought Caremark Rx Inc. for $27 billion. The combined companies became CVS Caremark Corp., the nation’s largest mail-order and retail medicine business.

On Thursday, the National Legislative Association on Prescription Drug Prices asked the U.S. Federal Trade Commission, which had to approve the deal before it took effect two years ago, to examine evidence of alleged “harmful and deceptive conduct” by CVS Caremark.

The legislative group alleges that pharmacy benefit managers (PBMs) with CVS Caremark “took rebates from manufacturers and did not pass them on to customers; suggested different, more expensive drugs and negotiated with employers and pharmacies separately, pocketing the difference,” Reuters reported.

In a letter to Jon Leibowitz, chairman of the FTC, the group alleged: “One investigation found that a PBM charged an employer $215 for a generic prescription but paid the pharmacy only $15. The PBM pocketed the $200 spread at the expense of the employer.”

“We believe that this evidence suggests that CVS Caremark has engaged in anti-competitive conduct that ultimately will harm both consumers and competition,” the letter said. “We urge the commission to open an investigation of CVS Caremark to explore whether there have been competition or consumer protection violations of the law.”

CVS fired back in a statement saying the association “has it exactly backwards.”

“The merger of CVS and Caremark is, in fact, making pharmacy health care more accessible, more effective and more affordable,” the company argued. “Our integrated pharmacy and PBM operations provide greater choice and more convenience for patients, improve health outcomes, and lower overall health care costs for plan sponsors and participants.”

The PBM business is an important and growing source of revenue for CVS. The company raised its 2009 earnings forecast earlier this week partly based on an estimate that its PBM revenue will increase by 15 to 17 percent this year, The Associated Press reported.

CVS also acquired RxAmerica LLC, a PBM company with more than 8 million members, as part of its purchase of Walnut Creek, Calif.-based Longs Drug Stores Corp. last year.

Earlier this week, CVS Caremark Corp. posted a profit of $738.4 million, or 50 cents a share, in the quarter that ended March 31, down 1.3 percent from the same period last year.