Internal investigators at the Environmental Protection Agency say the agency failed to follow peer-review guidelines when developing a key scientific document that underpins its greenhouse gas regulations.

The findings are likely to stoke Republican opposition to EPA's efforts to regulate greenhouse gases and could arm industry groups that are fighting the regulations in court. One prominent Republican is already calling for congressional hearings on the issue.

The document in question was developed by EPA and used to support its 2009 "endangerment finding." That finding concluded that greenhouse gases--including carbon dioxide, methane and nitrous oxide--pose a threat to public health. It paved the way for the EPA to begin developing greenhouse gas standards for refiners, power plants and other large emitters.

In a report released Wednesday, EPA's inspector general says the agency didn't follow federal guidelines for peer review when developing a 200-page scientific document to support its findings.

The impact of the inspector general's report on EPA's ability to develop new greenhouse gas rules, or to enforce existing rules, is unclear. Sen. James Inhofe (R., Okla.), a climate-change skeptic and the ranking Republican on the Senate's environment committee, is already calling for a congressional hearing to examine the findings.

The inspector general's report "confirms that the endangerment finding, the very foundation of President Obama's job-destroying regulatory agenda, was rushed, biased and flawed," Inhofe said in a statement.

The inspector general didn't evaluate the quality of EPA's science. It only reviewed the process the agency used for developing it. The inspector general noted that the National Research Council, one of the agencies that supplied EPA with scientific data, recently concluded that "climate change is occurring, is caused largely by human activities, and poses significant risks for a broad range of human and natural systems."