Eighteen Republican members of the Colorado State Legislature Monday sent a letter (pdf) to the U.S. Environmental Protection Agency (EPA) demanding the federal agency refrain from regulating the natural gas drilling practice of hydraulic fracturing, or “fracking,” no matter what a two-year EPA study of the process reveals.

Landowners and environmentalists around the country are increasingly concerned about instances in which they claim fracking has contaminated streams and drinking water sources. Oil and gas industry officials mostly resist attempts to further regulate the process, which was granted an exemption from the Safe Drinking Water Act during the Bush administration.

“The EPA shouldn’t stick its nose into the regulation of fracking or other oil and gas industry practices in states,” state Sen. Scott Renfroe, R-Greeley, said in a release. “Once the EPA completes its study, states should maintain jurisdiction over oil and gas operations.”

While the letter was addressed to the EPA, the matter is actually up to Congress, where U.S. Reps. Diana DeGette, D-Denver, and Jared Polis, D-Boulder, introduced the FRAC (Fracturing Responsibility and Awareness of Chemicals) Act in 2009. The bill requires full public disclosure of the chemicals used in the fracking process, which industry officials say amount to trade secrets.

Still, a growing number of companies are offering up some form of disclosure in order to head off looming federal regulation.

“Oil and gas employers have already been barraged by new regulations in Colorado, making it harder for them to do business in the state, particularly during these tough economic times,” Renfroe added, referring to amended drilling rules that went into effect last year and provide higher levels of public safety and environmental protection. “The last thing we need are further industry-crushing regulations out of Washington, D.C., that will cause even more lost jobs in Colorado.”

Proponents of those new regulations say the industry has actually gained greater regulatory certainty through the new drilling regs and that other states are all moving toward models similar to Colorado’s.

Republican state Rep. Randy Baumgardner, whose House District 57 includes heavily drilled Garfield County, also signed Monday’s letter.