Senators Ted Kaufman (D-DE) and Johnny Isakson (R-GA) introduced a measure in the Senate this week that would require the Securities and Exchange Commission to reinstate "the uptick rule."  The rule, which the SEC eliminated in 2007, restricts short selling.  Sen. Kaufman, in a press release from his office, blames the "abuse of naked short selling" for making the markets less stable:

“Abusive short selling is tantamount to fraud and market manipulation and must be stopped – now,” Sen. Kaufman said on the Senate floor this evening. “The uptick rule should have never been repealed. To permit people to sell shares they don’t have and won’t be able to deliver turns investment into pure speculation. The time has come for this practice to stop.”

Marketplace's Paddy Hirsch provides a clear explanation of the uptick rule, and how it works, in this Whiteboard video:

The Uptick Rule from Marketplace on Vimeo.