Republicans have seized on press reports that Treasury implemented the $50-billion bailout of the auto industry in a way that forced about 20,000 non-unionized workers at Delphi, a global auto parts supplier, to swallow significant cuts to their pensions. At the same time, Treasury helped ensure that the pensions of unionized workers were paid in full.

"As a result, Delphi's unionized retirees were made whole while salaried, non-unionized retirees saw their pensions reduced significantly," Issa and Turner wrote on Friday.

Issa and other Republicans wrote to Geithner on this issue in 2010 and 2011, but said Treasury so far has fallen far short of fully disclosing how the Delphi decision was made.

"Despite our repeated requests for all responsive documents and communications, the Treasury Department has only proffered a limited number of documents, many of which were already publicly available," they wrote. "Documents recently made public under the Freedom of Information Act, however, demonstrate that the Treasury Department was 'the driving force' behind the decision to terminate the pensions of Delphi's salaried employees.

"Given the substantial cost incurred by the administration in implementing this decision, the American people have a right to fully understand the process that led to it."

Issa and Turner again asked Geithner for "all records and communications" between Treasury and the White House's Automotive Task Force, the United Auto Workers, the Pension Benefits Guaranty Corporation, GM, Delphi and other public officials.