A House panel subpoenaed the Obama administration for documents surrounding what it says are $3.5 billion in improper payments to insurers to "prop up Obamacare."

The House Energy and Commerce Committee issued a subpoena on Monday for all documents on payments under Obamacare's reinsurance program. The subpoena is the latest step in an investigation by the panel into the payments, which Democrats charge is "overblown."

House lawmakers said that the payments are illegal and that the administration has stonewalled attempts to get documents.

"Congress should not have to issue subpoenas to get basic facts, but sadly that's become the case with the Obama administration," said Rep. Fred Upton, R-Mich., committee chairman.

The subpoena is in response to the administration refusing to produce the documents. The committee said in a press release that the administration wouldn't produce them due to "confidentiality interests."

The reinsurance program, which expires next year, was created to help insurers adjust to the new insurance markets created under Obamacare's exchanges. Insurers pay into the program and that funding is used to offset claims from the sickest patients.

Republicans have said that a portion of the funding, $3.5 billion, was supposed to go to the Treasury Department. However, Republican lawmakers said during an April hearing that the Centers for Medicare and Medicaid Services changed its position on the payments and diverted them to insurers.

CMS Acting Director Andy Slavitt said at the hearing the program isn't funded by taxpayers, but insurers.

He said that such a reinsurance program is quite common to ensure that people with large claims get covered.

The administration told the Washington Examiner that the program is intended to help reduce premiums for consumers while insurers adjust to the new market.

The Department of Health and Human Services "laid out its approach to implementing the reinsurance program as well as the legal rationale behind the approach through regulations that involved an extensive notice-and-comment process, and all the comments received were supportive of the policy," said spokesman Matthew Inzeo.

"Since then, HHS officials have responded to congressional questions about the program at several hearings and in multiple letters, and we will respond directly to the committee regarding its subpoena."

Democrats on the panel accused the Republicans of levying false charges, with Ranking Member Rep. Frank Pallone, D-N.J., saying at the hearing it was typical "overblown rhetoric and misinformation."