But grass-roots activists in the U.S. are upping the ante by demanding that Romney immediately reveal the names of the bankers and financial insiders attending his London fundraising events. In particular, they are pushing for the release of any and all information relating to Romney's interactions with donors associated with Barclays and any other institutions that have been linked to the LIBOR scandal.

The Center for Responsive Politics identifies Barclays as the largest source of campaign donations to Romney, and a Maine state legislator who has been in the forefront of campaign finance reform and corporate watchdog fights wants to know more about the relationship between Romney and the Barclays donors.

"Americans have a right to know who Romney's donors are so they can understand what policy agendas are in line with those donations," says Maine state Rep. Diane Russell, D-Portland. "We all have the right to donate to political campaigns, and the responsibility to own up to those donations. It's part of the democratic process."

Russell has started a national petition drive demanding that Romney come clean about the Barclays ties and the London fundraising event.

The "Mitt Romney: Reveal Your Secret Donors" petition reads: