House Republicans on Thursday called for a hearing to examine the Obama administration's decision to probe a major insurance company, at the behest of Sen. Max Baucus, over a mailer to customers about health care legislation -- a move they call a politically motivated "gag order" on critics of the Democratic plan. 

Republican criticism has swelled since the Centers for Medicare and Medicaid Services launched a probe into Humana, at the request of Baucus, D-Mont., over a mailer Baucus claimed misled seniors about proposed changes to Medicare. 

Humana, one of the largest private carriers serving seniors under the Medicare Advantage program, focused its mailer on the potential for cuts to the service, which were being debated in the Finance Committee on Thursday. 

Republicans say the administration was essentially punishing Humana for questioning the plan and firing a warning shot at any other companies that might be thinking of doing the same. The Department of Health and Human Services on Monday not only targeted Humana, but sent out a broad directive to all Medicare Advantage participants, telling them to "immediately discontinue all such mailings" and remove any such material from their Web sites. 

Robert Zirkelbach, spokesman for America's Health Insurance Plans, said the order went out to about 200 companies Monday night, just as the Senate Finance Committee was about to start debate on its version of health care reform. 

"This is an effort to stifle any dissent," he said.

"They are silencing opposition to the president's Medicare cuts," said Sage Eastman, spokesman for Rep. Dave Camp, ranking Republican on the House Ways and Means Committee. 

Camp and the other minority members of the House Ways and Means Committee wrote a letter Thursday to Chairman Charles Rangel, D-N.Y., urging a hearing in order to "investigate the unusual and potentially politically motivated decision by CMS to eliminate the flow of factual information from private health plans to their enrollees." 

The original Humana mailer said: "While these programs need to be made more efficient, if the proposed funding cut levels become law, millions of seniors and disabled individuals could lose many of the important benefits and services that make Medicare Advantage health plans so valuable."

It urged seniors to sign up with Humana for regular updates on the legislation and encouraged them to contact their lawmakers in Washington. 

Humana was expressing concern about proposals to cut Medicare and Medicaid spending by about $500 billion over 10 years -- including payments to Medicare Advantage plans by about $125 billion. 

Congressional Budget Office Director Douglas Elmendorf on Thursday agreed that seniors in the Medicare Advantage plans could see reduced benefits under Baucus' legislation. 

But Baucus said the proposed bill would not cut benefits. 

"I'm not going to let insurance company profits stand in the way of improving Medicare for seniors," he said in a statement, calling efforts to mislead seniors "wholly unacceptable." 

Democrats continued to assert that the company had made a false claim and that Republicans were again demonstrating their affinity for the insurance industry. 

Baucus said the mailer could be a violation of federal regulations. However, Republicans responded with Clinton administration guidance that prohibiting such information would violate basic freedom of speech and other constitutional rights of the Medicare beneficiary as a citizen.  

AARP, which also helps administer Medicare plans in conjunction with United Healthcare, has weighed in on that part of the health care debate as well -- only on the other side. 

The AARP continues to feature ads on an affiliated Web site defending the Medicare changes. One ad blasts critics for spreading "myths and scare tactics," and claims the reforms will not "hurt" Medicare but "actually strengthen it by eliminating billions of dollars in waste and lowering drug prices." Another AARP article declares, "Controlling the rising costs of Medicare doesn't mean cutting benefits." 

Eastman said AARP is not being held to the same standard. 

"If you're going to silence the critics you need to silence the proponents too," he said. "This clearly smacks of politics." 

A representative with the AARP could not be reached for comment.

FOXNews.com's Judson Berger and The Associated Press contributed to this report.