U.S. Sen. Jeff Flake (R-AZ) is among the Republican legislators urging the Treasury Department to disclose findings from its investigation into potential fraud by solar panel companies that received taxpayer-backed funding for over three years.

Earlier this year, Republican senators, led by Flake and Sen. Lisa Murkowski (R-AK) wrote a letter to Treasury officials demanding an update on the department’s probe into the allegations against solar companies that inflated their products' market value to get more taxpayer money.

Now, a political action committee has joined the call to action.

Last month, Citizens for the Republic, a committee that promotes limited government, maximum freedom and personal responsibility, among other principles, sent a letter to Sen. Thad Cochran (R-MS), chairman of the Senate Appropriations Committee, calling on Congress to look further into the issue.

“As heads of grass-roots organizations devoted to fiscal responsibility and government accountability, we urge Congress to launch an immediate investigation of Lyndon Rive, the chief executive officer of Solar City, and his brother Pete Rive, the company’s chief technology officer, for their $128.9 million cumulative compensation package while the company is simultaneously receiving more than half a billion dollars in federal direct grants and just as much, if not more, from state and local governments,” the letter said.

The committee said SolarCity has lost more than 50 percent of its value within the past year, and is only staying afloat because of government subsidies and a recent bailout by Elon Musk, a billionaire cousin of the Rives.

“Many American families are struggling to succeed and live the American dream, while SolarCity is receiving billions of dollars in taxpayer subsidies," the committee wrote. "It is for this reason that we are requesting an investigation of this compensation package and this solar model in general."

Treasury officials promised to release the department’s findings by June 2015 but never did. The Republicans contend that the potential solar energy fraud amounts to more than two-and-a-half times the amount of the Solyndra default.

Solyndra was a manufacturer of solar cells that was once praised for its unique technology. However, in 2011, the California-based company filed for bankruptcy after receiving $535 million from taxpayers in grants.

Since 2009, the Obama administration has given $25 billion in grants made by the Treasury Department to solar companies in an effort to promote green energy and combat global warming.

The grants, referred to as Section 1603 grants, funded 30 percent of solar energy investments and were part of President Barack Obama’s stimulus package. The grant program expired in 2011.

In addition to misrepresenting the fair market value of solar energy systems, federal auditors are concerned that some companies either double-dipped or exaggerated the size of their investments to get more money from the government.

But the three-year investigation by the department has left taxpayers with few answers.