Several Democratic senators recently have called for Johnson to resign, charging that he disregarded science and the law and may have misled them when he testified on Capitol Hill. Congressional committees are investigating whether the EPA's decisions have been made in accord with the conclusions of its staff and whether the White House interfered with some of the agency's work.
"I'm sensing there's built-up frustration among EPA employees," said one of the authors of the letter, Mark Coryell, president of the American Federation of Government Employees Local 3907, which represents staff members at the EPA's National Vehicle and Fuel Emissions Laboratory.
"Their best efforts to do right by the law and sound science have been subverted by actions taken by or not taken by Johnson, our administrator," Coryell said. "A lot of them are certainly hurt by the impact on their professional reputations."
The environmental group Public Employees for Environmental Responsibility gave a copy of the letter by Coryell and the others to McClatchy.
EPA spokesman Jonathan Shradar said Monday that the science of the document released last month "speaks for itself and the administrator is proud of the work the staff completed at his direction."
The Supreme Court in 2007 found that the EPA has the authority to regulate emissions of greenhouse gases from motor vehicles. The court said that under the Clean Air Act, the EPA should determine whether the emissions endanger the public and, if so, regulate them.
Johnson hasn't issued an endangerment finding. Last month, in response to the high court's ruling, he released a wide range of proposals by his staff for controlling greenhouse gas emissions and called for comment through Nov. 28.
But Johnson also argued that the federal Clean Air Act was "ill-suited" for regulating greenhouse gases, that the regulations would be "very complicated, time-consuming and, likely, convoluted," and that they'd be "relatively ineffective at reducing greenhouse gas concentrations given the potentially damaging effect on jobs and the U.S. economy."
In addition, Johnson attached letters from the White House's Office of Management and Budget and department secretaries in the Bush cabinet who disagreed with the EPA staff's proposals on legal, economic and scientific grounds.
The letter from Coryell and the other union officials said that EPA staff members who worked on the proposed regulations weren't given a chance to read the critiques or respond to them before the document was made public.
The letter said Johnson's actions were "troubling and, quite frankly, unprofessional," adding: "We believe EPA's hardworking, dedicated staff has earned more respect than you are giving."
The letter was dated July 30 and signed by Coryell and Silvia Saracco, president of American Federation of Government Employees Local 3347 at EPA's Research Triangle Park in North Carolina, and William Evans and J. William Hirzy, president and vice president, respectively, of National Treasury Employees Union Chapter 280 at EPA headquarters.
The union leaders also wrote that Johnson should release documents and testify as requested by Congress.