Few Supreme Court decisions have drawn as much ire from the Left as the Citizens United ruling in 2010. Throughout the last election cycle, they issued dire warnings that democracy would soon disappear amid a flood of corporate money.

But it wasn't just corporate money that Citizens United affected. The decision affected organized labor, as well -- and unions have taken full advantage of the changes. It may have made the difference in the last election.

According to data from the Center for Responsive Politics, Big Labor made about $13.5 million in so-called soft money donations to political action committees in the 2008 election cycle and slightly less, $12.5 million, in the 2010 off-year election. But in 2012, Big Labor's PAC donations shot up past $102 million -- a four-fold increase. The Service Employees International Union, for example, donated just a half-million in 2008. In 2012, it gave about $12 million. Other unions made up the rest.

"This is something Citizens United allowed," said Russ Choma, a spokesman for the center. "Just as it allowed corporations to give directly from their treasuries, it also allowed unions to give directly from their treasuries."

This is just a part of the money Big Labor spent on the election. More than $70 million was directly spent by the unions themselves on ads and other voter outreach in 2012. Choma adds that a lot of the Federal Election Commission reports by the unions are difficult for even the center to untangle, so the figures may not be complete. Nor do the FEC reports count the other unquantifiable contributions of unions to things like get-out-the-vote efforts.

In any event, the change brought by Citizens United was something that Big Labor pushed for all along. Back when the case was headed to the Supreme Court, the AFL-CIO filed an amicus brief "in support of the Appellant" -- that is, in support of Citizens United, the conservative media group that had been targeted by the FEC.

In its brief, the union coalition argued that the existing campaign spending laws violated free speech: "[L]abor organizations, including the AFL-CIO, and corporations, including Citizens United, remain subject to an unworkable censorship regime."

Prior to the decision, PAC donations had to be raised via individual contributions made by people within a corporation or union. There were limits on the amount of these contributions, too. The combination made raising money much harder.

The AFL-CIO was not acting in solidarity with Big Business. In the brief, it argued that unions have "crucial differences" from corporations -- namely that they are "democratic, member-controlled organizations, such that their campaign treasuries 'accurately reflect' members' support for their unions' political agenda."

What the AFL-CIO was getting at was that it wanted the Supreme Court to lift the campaign-spending restrictions only for unions, not for business. They got half a loaf: The court ruling threw out the restrictions on both corporations and unions.

Unions are taking full advantage. And contrary to popular belief, Big Business is not taking advantage of the ruling. "Certainly, Fortune 500 companies aren't making huge donations," says Sarah Byner, a researcher at the center. The big money on the Right is instead coming from individual moguls like Sheldon Adelson, not corporations. And they could have personally spent this money on elections even before Citizens United.

That doesn't mean that they are spending it wisely. As we saw, most of this raised by groups on the Right, such as Karl Rove's Crossroads groups, was wasted. Unions, on the other hand, focused their efforts on the key swing states like Ohio and Pennsylvania. After the election, AFL-CIO President Richard Trumka boasted: "We did deliver these states."

Unions have been very circumspect about Citizens United since the decision. They've even made a point of denouncing the Citizens United decision along with other liberal groups. But you'd think they -- and the Left -- would be grateful.

Sean Higgins (shiggins@washingtonexaminer.com) is a senior editorial writer for The Washington Examiner. Follow him on Twitter at @seanghiggins.