WASHINGTON -- Escalating an interstate fight that has been brewing for years, the entire Wyoming congressional delegation sent a letter to the Montana Board of Environmental Review urging it to reject a petition that would toughen standards for water flowing into Montana.

Sen. Craig Thomas, Sen. Mike Enzi and Rep. Barbara Cubin, all Republicans, jointly sent the letter late Friday, arguing that the new regulations would increase natural gas costs to the nation and harm Wyoming's coal-bed methane production. The letter also claimed that the new rules would provide no significant environmental benefit.

"The petition, under the guise of environmental benefit, could severely limit CBNG (coal-bed natural gas) production without any significant additional protection for water quality or existing water uses in Wyoming or Montana," they wrote. "The proposed rules lack scientific basis, pose a serious threat to energy supply, have questionable legal basis, and threaten ongoing cooperative efforts."

The Montana Board of Environmental Review began a rule-making process on the matter last year after Montana irrigators petitioned it to consider rules that would toughen the water-quality standards for discharges of coal-bed methane wastewater along waters that flow from Wyoming to Montana.

But the letter says that petition seeks to change the regulations "without any supporting science" and adds: "It appears that Wyoming CBNG exploration and development has been targeted."

The letter says such "apparent" targeting may be unconstitutional because only the federal government has the power to regulate interstate commerce.

The missive also cites a 2005 draft report by the EPA and the state of Montana as concluding that discharges in Wyoming have had no measurable effect on water quality in the Tongue River since coal-bed methane activity began in 1999.

But in a notice of a public hearing on the matter, the board wrote, "Montana's nondegradation policy will be critical to protect the existing water quality of rivers such as the Clark Fork of the Yellowstone, Rock Creek, Stillwater River, Flathead River, and the pristine streams of Park County if methane development occurs in these watersheds."

Coal-bed methane production involves pumping to the surface large volumes of groundwater in order to reduce pressure and release the gas stored within the coal. A small amount of such water goes into the Tongue, Powder and other Montana-bound waters.

Under the new rules, unless a waiver is granted, point sources of methane wastewater would have to achieve "zero discharge" of pollutants, accomplished by reinjecting the wastewater into the ground. If the geology of the area prevents reinjection, the water would have to be treated before being released.

The letter acknowledges legal issues surrounding whether the rule would be applicable in Wyoming but claims that if applied there, "evidence suggests that current and expected CBNG production in Wyoming would fall significantly."

Fearful of the higher costs of dealing with wastewater under the new rules, coal-bed methane producers have been fighting to stop the change. Wyoming Gov. Dave Freudenthal has backed them, but the letter marks the first time the congressional delegation has spoken out on the issue.

Irrigation districts, conservation groups, ranchers and others had petitioned the board to toughen the water standards, arguing that they should not have to accept lesser-quality water because of the coal-bed methane industry.