Three donors — Barbara Stiefel, Steve Mostyn and Franklin Haney — donated $1 million or more to the pro-Obama super-PAC in May. Mostyn is an attorney in Houston and a prominent Obama supporter, while Haney is chief executive officer of FLH Co., a real estate investment company. 

The Obama campaign has expressed concerns about the massive amount of cash flowing to outside spending groups. Conservative super-PACs and nonprofits have pledged to spend hundreds of millions of dollars to help Romney win the White House, while groups supporting Democrats have struggled to get off the ground.

Earlier this year, Obama reversed his opposition to super-PACs and gave his blessing to Priorities USA. His campaign urged wealthy donors to contribute to Priorities — run by former Obama aides Bill Burton and Sean Sweeney — and argued the campaign couldn’t “unilaterally disarm” in the fundraising race.