Top House Republicans were told in recent days that a former employee of their campaign committee may have forged an official audit during the contentious 2006 election cycle and that they should brace for the possibility that an unfolding investigation could uncover financial improprieties stretching back several years, according to GOP sources briefed on the members-only discussions....

“There is a sense that this could be very damaging to the committee,” said a Republican insider close to the GOP leadership. 

The precise details of the suspected accounting irregularities and their possible fallout are not entirely clear. NRCC officials and top GOP leaders are being tight-lipped in large part because the FBI is investigating the matter. An outside lawyer advising members and staff has warned everyone at the committee to keep quiet.