Here.  They are also accepting signatures.  I strongly agree with this from the new letter:

It cannot become our standard that where analysis and discussion of matters of public concern may cause offense, the social and institutional consequences of engagement are so costly that few will be willing to do the work. It cannot become our standard that the mere allegation of harm caused by some writing or speech, in the absence of any specific evidence to that effect, is sufficient to trigger such consequences. And it cannot become our standard that the mere fact that someone who causes harm agrees with something said or written by an academic is sufficient to saddle that academic with responsibility for that harm.

The Open Letter Concerning Transphobia in Philosophy is the latest depressing example of an increasing inclination in the Academy to adopt precisely these kinds of standards. The effect can only be to discourage those whom we employ to research, think, write, and speak about these issues from doing so and to deprive students of a diverse and intellectually rigorous education. This will neither benefit our laws, regulations, and public policies nor improve the education that students receive.