Sen. Jay Rockefeller (D-W.Va.) is fighting back against plans by the gang of six bipartisan Finance Committee health care negotiators to approve a bill with a nonprofit medical cooperative as opposed to a public insurance option.

Rockefeller, a senior member of the Finance Committee, has expressed dismay that the three Democrats and three Republicans on the negotiating team are leaning toward using a co-op to bridge the partisan divide on health care reform and mark up legislation that can garner broad support.

Rockefeller on Thursday announced that he was seeking more information on how co-ops work, sending letters to the Government Accountability Office, the National Cooperative Business Association, and the Department of Agriculture.

“I believe the inclusion of a strong public plan option in health reform legislation is a must — it is the only way to guarantee that all consumers have affordable, meaningful, and accountable options available in the health insurance marketplace,— Rockefeller said in a statement released by his office.

“There are real concerns about the potential impact of health care co-ops on consumers, and we cannot afford to hang our hat on any unproven, unregulated, or unreliable model for health insurance coverage.—

The co-op proposal was first offered by Senate Budget Chairman Kent Conrad (D-N.D.), who is one of the six negotiators, but it has gained currency with the Republicans in the group as well.

The three Republicans oppose the public insurance option. However, they believe the co-op proposal might offer an acceptable compromise.