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More than a dozen Republican lawmakers are pushing the Environmental Protection Agency to reconsider asserting regulatory authority over streams and wetlands amid intense backlash from farm groups over the agency's proposed water rule.

In a letter Thursday, the GOP senators faulted the EPA for announcing a proposed rule last week before the government's peer-reviewed scientific assessment was fully complete. They are calling on the government to withdraw the rule or give the public six months to review it, rather than the three months being provided.

The senators' move puts them among several groups -- from farmers and land developers to Western governors worried about drought management -- in expressing concern about a long-running and heavily litigated environmental issue involving the Clean Water Act that has invoked economic interests, states' rights and presidential power.

The letter was led by Sen. Pat Toomey, R-Pa., and signed by 14 other GOP senators.

"We believe that this proposal will negatively impact economic growth by adding an additional layer of red tape to countless activities that are already sufficiently regulated by state and local governments," the letter to EPA chief Gina McCarthy said.

Meanwhile, Rep. Steve Stockman, R-Texas, introduced appropriations language this week aimed at blocking the rule entirely. The proposed language states that "no funds shall be appropriated to study, promote, advertise, implement or otherwise promulgate" the rule.

“This new rule is another power grab by [President] Obama. This is a brazen attempt to impose a radical redefinition specifically rejected by Congress and the Supreme Court,” Stockman said in a statement. "Green radicals have tried for decades to pass this redefinition by law, but it was too radical to pass even a Democrat-controlled Congress."

Alisha Johnson, the EPA's deputy associate administrator for external affairs and environmental education, said the EPA's draft scientific assessment, used to inform the proposed rule, was being reviewed and wouldn't be complete until the end of this year or early next year. The EPA rule will not be finalized until the scientific assessment is fully complete, and will take into account public comments, she said.

The proposal would apply pollution regulations to the country's so-called "intermittent and ephemeral streams and wetlands" -- which are created during wet seasons, or simply after it rains, but are temporary.

At issue is the federal Clean Water Act, which gives the EPA authority to regulate "U.S. waters." Two Supreme Court decisions in 2001 and 2006 limited regulators' reach, but left unclear the scope of authority over small waterways that might flow intermittently.

Landowners and developers say the government has gone too far in regulating isolated ponds or marshes with no direct connection to navigable waterways.

Some 36 states, including Pennsylvania, have legal limitations that prevent the EPA from regulating waters not covered by the Clean Water Act, according to the Environmental Law Institute.

Tile drainage systems would not be regulated and there would be no new requirements for irrigation and drainage ditches. Exemptions already granted for farming activities would continue and 53 agricultural conservation practices would be added to the list.

But farmers who receive exemptions must also engage in an ongoing conversion practice that complies with Natural Resources Conservation Services standards, according to Stockman.

“Once the landowner completes the conservation practice or changes the use of his land, he loses his EPA exemption and must now comply with a new, and more complex, set of rules,” Stockman said. "In other words, the only way a farmer or rancher can exempt himself from the EPA rule is to adhere to a mountain of other new federal rules."

Criticizing the proposal as a "serious threat" to farmers, the American Farm Bureau Federation said Wednesday that the rule would impose new regulatory burdens on farmers, ranchers and other landowners and give the agency veto power over a farmer’s ability to work.

"This is not just about the paperwork of getting a permit to farm, or even about having farming practices regulated. The fact is there is no legal right to a Clean Water Act permit—if farming or ranching activities need a permit, [the] EPA or the Army Corps of Engineers can deny that permit," the group said in a statement.

The proposed regulation, broadly supported by environmental groups, has become a charged political issue in a midterm election year where President Obama has pledged to use his executive power as needed to push through environmental and climate change protections.

"It's the most breathtaking power grab I've seen in a long time, and they wonder why the economy is so weak," Toomey said in a Philadelphia radio interview this week.

Still, the issue is not divided strictly along partisan lines.

The proposed rule has drawn the concern of Democratic Colorado Gov. John Hickenlooper, chair of the Western Governors Association. He has warned federal officials that the rule change could impinge upon state authority in water management and that states should be consulted in the EPA decision-making. In recent years, Hickenlooper has urged the Obama administration to speed approval of water projects because of a looming water supply gap in Colorado.

The Associated Press contributed to this report.