A futures regulator proposal that would place position limits in the commodities markets may not prevent manipulation or speculation, and would prevent operators of commodity funds from meeting their investment goals, an exchange-traded fund manager said.

The U.S. Commodity Funds, a manager of leading ETFs U.S. Oil Fund and U.S. Natural Gas Fund , said on Friday that instead of preventing excessive speculation -- the goal of position limits -- it could adversely affect the value of the exchange-traded pools managed by it and others.

Position limits will hamper the ability of USCF and other managers of publicly traded, unlevered, passive commodity funds to prudently meet the investment objectives of the commodity pools that they manage, USCF said in a comment letter to the U.S. Commodity Futures Trading Commission.

(Editing by Alden Bentley)