The American Hospital Association wants the U.S. Justice Department to block the merger of Pennsylvania's two biggest health insurers.

The hospital advocacy organization expresses concern that the combination of Pittsburgh's Highmark Inc. and Philadelphia's Independence Blue Cross would lead to a "huge accumulation of market power."

You can read the association's letter to the Justice Department here.

It's been more than a year since the two big insurers announced they wanted to merge. Pennsylvania's Insurance Department has yet to hold hearings on the transaction, but officials indicate that they will likely occur this summer.

The American Hospital Association represents 5,000 hospitals, including many in Pennsylvania that fear a bigger insurer would be able to cut reimbursement for health-care services. The letter says:

An IBC/Highmark combination could easily use its enormous market power to drive reimbursement below competitive levels and to force anticompetitive contract terms on providers.

The association also says that if a bigger Blue Cross gets too powerful "advances in quality and performance" at hospitals could be limited. It also questions whether any of the savings from the combination would ever trickle down to consumers.

As of last December, the Pennsylvania Insurance Department said that it could render a final decision on the combination by the end of 2008.