The United States Natural Gas Fund suspended issuance of new shares because it ran out of them, Bloomberg reports on Tuesday.

The fund is the largest exchange-traded fund in natural gas and allows traders to buy shares that track the fuel.

Traders have invested millions in the fund, increasing its popularity. But it won't be issuing shares until it gets permission to register 1 billion new shares from the Securities and Exchange Commission, the Commodities Futures Trading Commission, the Financial Industry Regulatory Authority and the National Futures Association, the news agency reports. The request was filed since June 5.

On Tuesday, trading ended after 2:20 p.m. Shares fell more than 2 percent or 31 cents to $12.25