Sen. Jay Rockefeller (D-WV) has a proposition: If the government is going to mandate that Americans buy health insurance from private companies, they should know how much of that money actually goes to paying health insurance costs. And insurers aren't happy about it.

On Friday, Rockefeller sent letters to executives at the 15 largest health insurance companies in the country, asking them to compile data on this question for the Senate Commerce Committee by September 8.

"It's another page out of the same playbook," says Robert Zirkelbach, spokesman for America's Health Insurance Plans. "There's an effort to shift the focus to the health insurance industry rather than on the bills in Congress."

When Rep. Henry Waxman (D-CA) asked for similar information regarding executive compensation at private health insurance companies, AHIP called it a "fishing expedition."

If Rockefeller wants info on what's known as the medical-loss ratio, Zirkelbach says, "health insurers already provide that information to state insurance commissioners, federal regulators, and the SEC."

AHIP's response is indicative of the industry's position on the inquiry. But the decision of whether to comply with Rockefeller's (or Waxman's) inquiry will fall to individual executives.

Rockefeller is a committed reformer, and a member of the Senate Finance Committee. But he's been largely shut out of the panel's health care negotiations for several weeks.