Although Donald Trump just lined up Silicon Valley billionaire Peter Thiel for a Republican National Convention speech, a new open letter makes it clear that much of the tech industry remains concerned about the prospect of a Trump presidency.

In the letter, posted today to Medium, luminaries of Slack, Facebook, Instagram, and several other companies and organizations say that "Trump would be a disaster for innovation." Signers include high-profile names like Tim Wu, Steve Wozniak, Stewart Butterfield, Padmasree Warrior, Esther Dyson, and Ev Williams. Katie Jacobs Stanton, a former Twitter exec who is now the CMO of Color Genomics, published the letter.

Citing Trump's immigration policies, hostility toward the media, and recent suggestion that he would consider "shutting down" parts of the internet, the group writes that Trump's policies would risk "distorting markets, reducing exports, and slowing job creation."

"His vision stands against the open exchange of ideas, free movement of people, and productive engagement with the outside world that is critical to our economy — and that provide the foundation for innovation and growth," the group writes.

"We stand against Donald Trump's divisive candidacy and want a candidate who embraces the ideals that built America's technology industry: freedom of expression, openness to newcomers, equality of opportunity, public investments in research and infrastructure, and respect for the rule of law," the letter concludes. "We embrace an optimistic vision for a more inclusive country, where American innovation continues to fuel opportunity, prosperity and leadership."