By Sam Baker - 05/14/13 09:17 PM EDT
The lawmakers asked for detailed information about Sebelius's outreach to industry groups and whether private funds also went to HHS accounts.
Two House committees launched similar investigations Monday.
“Our initial reaction is that this appears at best to be an inherent conflict of interest and at worst a potentially illegal augmentation of appropriation," the senators wrote.
Sen. Lamar Alexander (R-Tenn.) has compared the fundraising to the Iran-Contra scandal, in which Congress refused to provide funding for Nicaraguan rebels, so officials in the Reagan administration raised private money for the fighters.