WASHINGTON -- Republicans on a House Energy and Commerce Committee panel on Thursday overrode vigorous Democratic objections and took the apparently unprecedented step of authorizing subpoenas for internal White House communications related to a $500 million taxpayer loan guarantee for the failed solar company Solyndra.

Rep. Diana DeGette of Colorado, ranking Democrat on the panel, called it a "sad day" for the committee and "an act of irresponsible partisanship," stressing that the committee had never before subpoenaed the White House.

Republicans said they had hoped to avoid the step but that the committee's long-running investigation had failed to get to the bottom of why Solyndra, which collapsed in August and is now under criminal investigation, was selected to receive the Obama administration's first loan guarantee under the stimulus act. President Barack Obama last year visited the company's California operation, whose biggest investors were venture capital funds linked to Tulsa billionaire George Kaiser, a major Obama fundraiser.

Some Republicans have questioned whether the administration rushed stimulus funding out the door to benefit its political supporters. On Oct. 14, the White House told the committee that it would not comply with a request for all internal White House communications regarding the Solyndra loan.

Following the vote, a White House official said the administration had cooperated extensively with the committee's investigation, producing more than 85,000 pages of documents, including 20,000 pages Thursday afternoon, and having administration officials provide multiple briefings and hearings.

"The White House has also already provided over 900 pages of documents in response to requests we have received. And all of the materials that have been disclosed affirm what we said on day one: This was a merit-based decision made by the Department of Energy," White House spokesman Eric Schultz said.

Solyndra, a Silicon Valley solar panel maker, was a centerpiece of Obama's initiative to develop clean technologies and received the program's first loan guarantee, for $535 million. It later collapsed.