The organization was given a $10,000 donation from Midler's family foundation, which tax experts say isn't allowed allowed to donate to super-PACs because of the way it's set up. A spokesman for Giffords's organization tells the Center for Public Integrity it is in the process of returning the money.

"These are not illegal contributions for us to take, but it’s our understanding that the donations are not appropriate for the donors to make," Americans for Responsible Solutions spokeswoman Katie Hill told CPI. "Thus, we are processing refunds, which will be disclosed on our next report."

Giffords's group was a major player in the gun control debate earlier this year, running ads advocating for background checks that targeted a number of lawmakers in both parties.