NEW YORK -- New York City Mayor Michael Bloomberg has been an influential voice in the debate over the natural gas drilling method known as hydraulic fracturing.

His opposition to "fracking" near the city's drinking water reservoirs led to a state ban on drilling in the watershed.

But Bloomberg has now endorsed gas drilling in a letter to The Washington Post, co-written with George Mitchell, a pioneer of fracking techniques.

The pair say a natural gas boom would spur economic growth, cut energy costs and reduce reliance on dirtier fuels like coal.

But they also wrote that fracking should only be done under strong environmental regulations.

Bloomberg's foundation said Friday that it would give $6 million to the Environmental Defense Fund to help push for those regulations in 14 gas producing states.