Union of Concerned Scientists
The Union of Concerned Scientists (UCS) takes the liberal side on of the nuclear arms race and the environment.
Founded by physicist Henry Kendall, UCS began as a collaboration between students and faculty members at MIT in 1969.  It includes some fifty thousand scientists and citizens across the United States.
Its early work focussed on challenging the safety of nuclear power plants and intervening in their licensing hearing. They were one of the most active critics of Ronald Reagan's Strategic Defense Initiative.
They accused the Bush administration of suppressing science, but without giving a single example. Instead, they simply cited a survey in which 8% of scientists said their work had been "changed". (This is based on a survey sent to 1,600 scientists; 1,292 didn't even fill out the survey.)
John Marburger said:
- "Many of its statements and conclusions … were perverse oversimplifications of complex issues. .... I think it's hard, maybe impossible, for an advocacy organization to be entirely science-based." 
- About UCS - official website