During the primary season, tech industry leaders kept fairly quiet on the subject of the presidential race and its most notorious contender, Donald Trump. A few investors snarked about him on Twitter, and his campaign netted minimal donations from Silicon Valley. But now, many CEOs are denouncing the presumptive nominee in an open letter.

“We have listened to Donald Trump over the past year and we have concluded: Trump would be a disaster for innovation. 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 letter says. It’s signed by an impressive list of executives from Slack, Twilio, Yelp, Reddit, Twitter, and more.

The letter chides Trump for his positions on immigration and a free and open internet, saying that his policy proposals would have a negative effect on the tech industry. The group of CEOs, investors, and policy advisors argue that immigration drives entrepreneurship, noting that 40 percent of Fortune 500 companies are founded by immigrants and the children of immigrants. “We believe that America’s diversity is our strength,” the letter says.

Tech leaders also take issue with Trump’s calls for shutting down the internet. At a Republican debate last fall, Trump said he would consider closing off internet access in countries with which America is at war. “I sure as hell don’t want to let people that want to kill us and kill our nation use our internet,” Trump said. The letter says that such a proposal demonstrates “both poor judgment and ignorance about how technology works,” and that it demonstrates Trump’s penchant for censorship.

Although the open letter is signed by nearly 150 people, signatures from employees of some of the largest tech companies — Facebook, Apple, and Google — are notably sparse. Google’s Vint Cerf is a signatory, but he is listed simply as an “internet pioneer” rather than a Google employee. Apple co-founder Steve Wozniak, an outspoken critic of Trump, also added his name to the list. Only one current Facebook employee, vice president of product design Margaret Stewart, signed the letter, but she is not joined by Mark Zuckerberg. Zuckerberg subtly criticized Trump at Facebook’s F8 conference for the exact points highlighted in the letter, but has also faced criticism himself over claims that Facebook censored conservative media outlets.

The absence of Google and Facebook leaders from the letter is likely driven by the companies’ desires to remain neutral on political events. Despite Zuckerberg’s veiled criticism of Trump, Facebook remains a sponsor of both the Republican and Democratic National Conventions. Google is also chipping in sponsorship dollars to the RNC.

Even without support from the likes of Zuckerberg and Tim Cook, the list of supporters of the letter is striking and diverse, including an MIT professor and former FCC chairman alongside major CEOs and investors. The letter is cross-posted to the Medium accounts of several of the writers, including Yelp VP of public policy Luther Lowe. (The letter is also signed by Yelp CEO Jeremy Stoppelman and SVP of engineering Michael Stoppelman.) But Lowe says Yelp didn’t lead the effort to write the letter — rather, it was collaboratively written by the group.

The letter also bears the signatures of some of Hillary Clinton’s most outspoken Silicon Valley supporters. Joyus CEO Sukhinder Singh Cassidy and Hyperloop One executive chairman Shervin Pishevar have each hosted big-dollar fundraisers for Clinton and signed their names to the letter. Chris Sacca, a candid Clinton supporter and donor, also signed on.

However, the letter stops short of endorsing Clinton and merely denounces Trump’s candidacy.

“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. We embrace an optimistic vision for a more inclusive country, where American innovation continues to fuel opportunity, prosperity and leadership,” the letter says.

The full list of signatories is below:

This post was updated on 7/15 to clarify Yelp’s role in drafting the letter.