Updated

At first blush, the Supreme Court's ruling last week striking down longstanding campaign finance restrictions seemed good news for any entity looking to spend its money more freely in the political arena -- including labor unions.

In its 5-4 decision, the high court threw out parts of a 63-year-old law that said companies and unions could be prohibited from using their own money to produce and run campaign ads for or against particular candidates.

But many unions are now complaining that the controversial decision is not a win for any group other than big business. They say that even though the decision allows freer spending across the board, corporations have an unfair advantage -- they have more money to spend.

"The four largest Wall Street banks, if they expended one-tenth of 1 percent of their resources in a political campaign, that would eclipse every single penny of union revenue for every union in the country," said Leo Gerard, president of United Steelworkers International.

According to campaign finance data, businesses spent $1.96 billion in the 2007-2008 cycle, while labor and other interest groups spent $673.47 million.

Jessica Levinson, director of political reform at the Center for Governmental Studies, suggested that under the court's decision, smaller groups would be overwhelmed by the political influence of major corporations.

"The issue with this decision is, now that corporations can tap into their general treasury funds, will smaller corporations, smaller nonprofit corporations, labor unions and individuals be able to have a voice in elections?" she said.

However, while corporations far outspent unions and other interest groups in the last cycle, that spending, historically, has not benefited one party over the other.

Since 1990, corporations have divided their contributions nearly equally -- 49.4 percent toward Democrats and 50.6 percent toward Republicans.

Union political spending is not so balanced. In the same period, labor unions gave 92 percent of donations to Democrats, while just 8 percent went to Republicans.

With the Obama administration and congressional lawmakers vowing to pass legislation to undermine the Supreme Court's decision, union leaders are starting to get on board.

Union leaders said Monday they are very supportive of Sen. Russ Feingold's, D-Wis., plan to quickly pass legislation to impose new restrictions on campaign finance -- though the heavy congressional workload could make it difficult to push such a package through anytime soon.

Fox News' Shannon Bream contributed to this report.