Updated

After the federal government put up hundreds of billions of dollars to bail out Wall Street, the largest labor union in America wants those firms to return the favor.

The AFL-CIO reportedly is promoting a proposal to tax every single stock transaction, and it's gained some support among Democrats.

According to The Hill, the tiny tax would be about a tenth of a percent -- but it could mean a lot of money for companies, like Goldman Sachs, that are making billions and conducting a high volume of trades.

Union policy director Thea Lee told the newspaper that the tax could raise between $50 billion and $100 billion annually for the federal government, but also serve to discourage "speculative financial activity." In other words, the kind of lightning-fast trading conducted by mega-firms which critics say leads to volatility.

The idea reportedly is gaining some support in Congress and among top officials in London.

But Mark Calabria, director of financial regulation studies at the Cato Institute, said such a tax would not be a big enough deterrent to change Wall Street behavior in any significant way.

"The gamblers out there, the speculators, I don't think it's going to necessarily deter them," he said. "It's just another way to raise revenue. It really has no other value."

Click here to read the story in The Hill.