Citizens United money -- the campaign contribution money allowed by the Supreme Court decision -- has flooded the Romney campaign since Labor Day, with the Republican contender receiving 70% of outside spending, according to an analysis released Wednesday from the Center for Public Integrity.

Based on data from the Federal Election Commission, the Center for Public Integrity reports that "more than $106 million of the $117 million spent on the Obama-Romney matchup since Sept. 3 has been on negative ads, with President Barack Obama absorbing more than $80 million in attacks."

Citizens United money has flooded campaign spending with $217 million just since Labor Day, the group adds, with $119.9 million of that coming from super PACs.

While the creation of super PACs and the money they've poured into elections has received attention in the wake of the Citizens United decision, these groups no longer have a monopoly on outside political spending.

The Center for Public Integrity reports that $95.9 million of the $217 million spent since Labor Day comes from nonprofits. 

A recent report from national research and advocacy organizations Dēmos and US PIRG showed that money from 501(c)(4) nonprofits, what they call “dark money” groups for their lack of transparency, actually outspent super PACs in the 2010 cycle by a substantial margin and are set to have an even greater effect on this year’s elections.

Adam Lioz, Counsel for Dēmos and report co-author, said of the campaign spending by super PACs and nonprofits: “The more money they pump in, the louder they’re able to amplify their voices—until a few wealthy individuals and interests are dominating our public square, drowning out the middle and working classes.”