In a move some fear is a reprisal for opposing President Obama's health care plan, Democrats sent 52 letters to health insurers requesting financial records for a House committee's investigation.

Reps. Henry Waxman, D-Calif., and Bart Stupak, D-Mich., sent a letter warning health insurers that the House Energy and Commerce Committee is "examining executive compensation and other business practices of the health industry."

Waxman, chairman of the committee, and Stupak, chairman of the Oversight and Investigations Subcommittee did not inform their Republican counterparts of their plans.

Health insurers have until Sept. 4 to provide Congress a detailed list of every employee who made over a $1 million dollars a year between 2003 and 2008. Democrats also want documents about conferences and any events held off company property as well as the types of transportation, lodging, food, entertainment and even gifts exchanged.

Raising the intimidation stakes: the Waxman letter offers insurers no explanation of what is being investigated or why.

Industry insiders fear the beginning of reprisals for anyone daring to dissent from the Obama agenda. One said it feels like a reprisal audit by the IRS.

With raucous health care town halls unfolding nationwide during the August congressional recess and polls showing increased opposition to a government-run insurance program or "public option," neither Waxman nor Stupak nor their staffs would comment on this story. But it's no secret that Democrats blame anti-reform ads on the private health insurance industry and its supporters.

Private health insurers warn that a public option could put them at a competitive disadvantage and even out of business, but they insist they support health care reform in general.

A spokesman for Stupak told The Associated Press Tuesday night that 52 letters had been sent to health insurers with $2 billion or more in annual premiums. He said letters were not dispatched to other industry groups, some of which have been airing television advertising in support of Obama's call for legislation.

But Robert Zirkelbach, spokesman for the American Health Insurance Plans, said Democrats on the panel hoped to "silence the health insurance industry and distract attention away from the fact that the American people are rejecting a government-run plan" as part of Obama's planned overhaul.

Zirkelbach said it would be up to individual companies to decide whether to turn the records over.

Spokesmen for three large insurance companies, Aetna, UnitedHealth Group Inc. and WellPoint Inc., confirmed the firms had received the letters but declined comment.

FOX News' Carl Cameron and The Associated Press contributed to this report.