With silver prices falling this past summer, silver bugs world-wide set out to prove that their metal was in short supply and market manipulation was at work. They bombarded federal regulators with hundreds of emails crying foul play and demanded answers.

Though such pleas proved futile in the past, this time the rousing chorus grabbed regulators' attention. On Wednesday, the Commodity Futures Trading Commission confirmed that there's an investigation into the silver market.

The CFTC isn't yet convinced there's systemic wrongdoing and in May published a report saying as much. But the agency decided to take a fresh look, in part to show critics that it checks out complaints, and also to make sure there isn't something new to uncover.

"We take the threat of manipulation in the futures and options markets very seriously and employ a number of measures to prevent, identify and prosecute it," said Stephen Obie, acting director of the agency's division of enforcement.

Silver investors have argued that a handful of U.S. banks have been controlling a large portion of silver's short positions -- or bets that prices will decline -- on Comex division of the New York Mercantile Exchange. Official data from the CFTC showed that two U.S. banks had increased short positions in the silver futures market between July and August by 450% and controlled 25% of the total open interest.

"The proof that this selloff was criminal lies in public data," wrote Theodore Butler of Cape Elizabeth, Maine, in August in a silver newsletter. "The concentrated sale of such quantities in such a short time" caused silver's fall, wrote Mr. Butler, who for many years has been vocal about purported silver-market manipulation. In September he reiterated to readers that they should email the CFTC.

The CFTC had argued in May that the large banks that people assailed for manipulating the market were instead acting appropriately as market makers, who take on futures positions to offset their exposure in over-the-counter markets. Therefore, these traders aren't "naked shorts" and won't benefit from long-term depressed silver prices. Many analysts agree with the agency's conclusion.

Silver stalwarts weren't persuaded. Jason Hommel, a newsletter writer based in Penn Valley, Calif., directed readers to visit their local coin shops at 2 p.m. on Sept. 2 to size up for themselves whether there was a silver shortage. From Michigan to North Carolina and beyond, he says, investors trekked to coin shops. Many reported no silver for sale.

Bart Chilton, one of the CFTC commissioners, said he has received about 700 emails from silver investors since August, far more than the estimated 100 he received from May to July. Mr. Chilton, a Democrat who has criticized the CFTC as doing a poor job communicating with consumers, says he has spent nights and weekends personally answering emails.

Historically, silver has been a volatile market. This year it saw a near-50% drop and remains down 9.5% on the year. Gold is up 6.5%. The agency has long heard from frustrated silver investors. In 2004, it published an open letter by Michael Gorham, then the agency's director of market oversight, after receiving more than 500 letters and emails from silver investors.

That the enforcement rather than oversight division is taking on the issue marks a difference from the CFTC's previous efforts regarding the silver market. The oversight division performs overall market surveillance. The enforcement division looks at activities in a specific time period.