This began from a controversy where Anima Anandkumar (https://en.wikipedia.org/wiki/Anima_Anandkumar), Director of AI at nvidia, posted a list of people she blocked on Twitter, encouraging her followers to "cancel" them. I wrote more about this and linked to her tweets in a past discussion at https://news.ycombinator.com/item?id=25419871, but Anima Anandkumar has since deleted her tweets and then her account.

One of her targets is Pedro Domingos, who is a professor at the University of Washington and a well-known expert in the space (he authored "The Master Algorithm"). Domingos is also known for being against the infiltration of "woke" culture into academic institutions, because it corrupts the purity of research and introduces political biases. This came up recently because NeurIPS (an AI conference) is going to require an "impact statement" for all submitted research papers, which has raised concerns about political bias at the conference, since researchers will likely include pandering progressive impact statements just to get through the process without controversy. Anandkumar has been one of the prominent activists pushing for NeurIPS to include impact statements, and was formerly involved in a campaign to push NeurIPS to be renamed from NIPS to NeurIPS (https://www.wired.com/story/ai-researchers-fight-over-four-l...).

This new letter to ACM was already discussed on Hacker News (see https://news.ycombinator.com/item?id=25575321). The letter includes Domingos as an initial signatory, and the group the letter is being sent to (Communications of the ACM) lists Anima Anandkumar (who tried to cancel him) on their Editorial Board (https://cacm.acm.org/about-communications/editorial-board/).

Seeing the name of Pedro domingos and how he got cancelled for expressing his views in the recent incident involving Google and timnit gebru, makes me think it's probably related to that.