Federal regulators are extending, for four months, the curbs put in after the May 6 market plunge that briefly halt trading of some stocks that make big price swings.

The Securities and Exchange Commission on Thursday approved the request of major U.S. exchanges to extend through April 11 the so-called "circuit breakers" in a six-month pilot program that would have ended Friday. Under the rules, trading of any Standard & Poor's or Russell 1000 stock that rises or falls 10 percent or more within a five-minute span is halted for five minutes.

The circuit breakers were installed to help prevent another disruption like the "flash crash" in May, which saw the Dow Jones industrial average drop nearly 1,000 points in less than a half-hour. SEC Chairman Mary Schapiro has said they have worked well but "may need to be further enhanced."