The text of the letter may be found here.
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We, the undersigned faculty members at Iowa State, reject all attempts to represent Intelligent Design as a scientific endeavor.
Advocates of Intelligent Design claim the position of our planet and the complexity of particular life forms and processes are such that they may only be explained by the existence of a creator or designer of the universe.
Such claims, however, are premised on 1) the arbitrary selection of features claimed to be engineered by a designer; 2) unverifiable conclusions about the wishes and desires of that designer; and 3) an abandonment by science of methodological naturalism.
Methodological naturalism, the view that natural phenomena can be explained without reference to supernatural beings or events, is the foundation of the natural sciences. The history of science contains many instances where complex natural phenomena were eventually understood only by adherence to methodological naturalism.
Whether one believes in a creator or not, views regarding a supernatural creator are, by their very nature, claims of religious faith, and not within the scope or abilities of science. We, therefore, urge all faculty members to uphold the integrity of our university of science and technology, and convey to students and the general public the importance of methodological naturalism in science and reject efforts to portray Intelligent Design as science.
Hardly the "vicious attack" Gonzalez refers to.