Solyndra's CEO Brian Harrison and Chief Financial Officer W.G. Stover sent letters to the House Energy and Commerce Committee on Tuesday saying they will not answer questions when they appear on Capitol Hill.
The letters cite the FBI's ongoing criminal investigation.
Republican leaders said they were dismayed that Harrison and Stover had reneged on earlier promises to testify.
The House committee is investigating a $528 million loan Solyndra received from the federal government in 2009.
"It's disappointing that the officials who canvassed the halls of Congress in mid-July and misled our members about the financial state of their company are now unwilling to answer direct questions, but any effort to cover up the truth will ultimately not succeed," Reps. Fred Upton and Cliff Stearns said in a statement.
The Silicon Valley company was the first renewable-energy company to receive a loan guarantee under the stimulus law, and the Obama administration frequently touted Solyndra as a model for its clean energy program.
Solyndra declared bankruptcy on Aug. 31 and layed off 1,100 workers.
The Associated Press contributed to this report.