Then again, most of Obama’s supporters don’t pay taxes so it’s not like they care.

Washington — The U.S. Treasury said Wednesday it plans to sell 30 million additional shares of General Motors stock in a new public offering in conjunction with GM’s return to the S&P 500 index on Thursday.

The United Auto Workers Retiree Medical Benefits Trust — which holds about 14 percent of GM — will also participate by selling 20 million shares, making the total offering size 50 million shares. It represents about 12 percent of Treasury’s outstanding GM stock.

The move may mean that Treasury completely exits in 2013, rather than by the end of March 2014. The return to the S&P will prompt significant demand for GM shares and the stock has recently traded near its highest level since February 2011. GM is filing a new prospectus ahead of the sale.

The Treasury sold nearly 20 percent of its remaining shares in General Motors Co. in the first three months of the year, the Detroit automaker disclosed Thursday.

The Treasury, which initially held 60.8 percent of GM as part of the U.S. $49.5 billion bailout, now owns just 16.4 percent, or 241.7 million shares. In December, the Treasury sold GM 200 million shares of its stake for $5.5 billion to reduce its stake to 300 million shares.

In total, Treasury has recouped $30.6 billion. At current trading prices, Treasury would lose around $10 billion on its GM bailout.