After President Trump put a travel ban in place affecting seven Muslim-majority countries, tech executives roundly and publicly denounced the move.

Immigrants have played a big role building some major U.S. companies, particularly in tech. A 2011 report from the Partnership for a New American Economy estimates that 45% of high-tech companies in the Fortune 500 were founded by first- or second-generation Americans.

Apple CEO Tim Cook

Cook issued a letter, which was obtained by CNN, reacting to what he called "deep concerns" among employees. He assured workers that Apple does not support Trump's policy and the company is prepared to lend them aid.

"Apple would not exist without immigration, let alone thrive and innovate the way we do," Cook said.

Google

Google sent out a memo to its employees urging anyone with a visa or green card from one of the banned countries to cancel any travel plans.

"Please do not travel outside of the U.S. until the ban is lifted. While the entry restriction is currently only in place for 90 days, it could be extended with little or no warning," the memo, which was reviewed by CNN, reads.

Microsoft executive Brad Smith

Microsoft said it employs 76 people that could be affected by the ban. Smith said in an email to employees, which was shared by Nadella on LinkedIn, that it will provide "legal advice and assistance" to those affected.

Twitter CEO Jack Dorsey

Dorsey called the potential impact of Trump's decision "real and upsetting."

The Executive Order's humanitarian and economic impact is real and upsetting. We benefit from what refugees and immigrants bring to the U.S. https://t.co/HdwVGzIECt — jack (@jack) January 28, 2017

Chorus CEO Dick Costolo

Chorus CEO and former Twitter chief executive Costolo called Trump a "a coward" on Saturday.

Salesforce executive Vala Afshar

Afshar tweeted a list of U.S. tech companies that were founded by immigrants, including Apple (AAPL), Google (GOOG) and IBM (IBM).

US tech companies founded by 1st/2nd generation immigrants 🇺🇸



Apple

Google

Facebook

Amazon

Oracle

IBM

Uber

Yahoo

EMC

eBay

AT&T

Tesla

Reddit — Vala Afshar (@ValaAfshar) January 28, 2017

Y Combinator cofounder Paul Graham

Graham weighed in, saying, "This is a good time to remember that without immigration the U.S. will only have 5% of the top people in each field."

This is a good time to remember that without immigration the US will only have 5% of the top people in each field. https://t.co/px0bA0Ou9x — Paul Graham (@paulg) January 28, 2017

Y Combinator president Sam Altman

Altman criticized Trump's move in a blog post. He called on tech executives to publicly speak out against Trump's executive order "at a minimum."

Time to Take a Stand: https://t.co/xHs5fV6PYP — Sam Altman (@sama) January 28, 2017

LinkedIn CEO Jeff Weiner

Weiner said "all ethnicities should have access to opportunity, calling it a "founding principle" of the U.S.

40% of Fortune 500 founded by immigrants or their children. All ethnicities should have access to opportunity -- founding principle of U.S. — Jeff Weiner (@jeffweiner) January 28, 2017

Yelp CEO Jeremy Stoppelman

Stoppelman called it a "sad day" for America.

Agreed. Sad day for USA. https://t.co/SikAaNVeAm — Jeremy Stoppelman (@jeremys) January 28, 2017

Investor Chris Sacca

Shark Tank star and tech investor Chris Sacca promised to match up to $50,000 worth of donations to the ACLU.

I can barely keep up with the replies. Thank. You. All. 🇺🇸



But it's clear we're gonna need a bigger boat...



So I'll match up to $50k. https://t.co/R3ttnbwgMV — Chris Sacca (@sacca) January 28, 2017

Box CEO Aaron Levie

Levie also promised to donate to the ACLU and called Trump's actions "immoral."

On every level -moral, humanitarian, economic, logical, etc.- this ban is wrong and is completely antithetical to the principles of America. — Aaron Levie (@levie) January 28, 2017

Path CEO Dave Morin

Morin called it "one of the weakest decisions in American history."

In the long term, today will reflect one of the weakest decisions in American history. — DAVE MORIN (@davemorin) January 28, 2017

Salesforce CEO Mark Benioff

Benioff retweeted numerous anti-ban sentiments before posting his own thoughts.

When we close our hearts & stop loving other people as ourselves (MK 12:31) we forget who we truly are---a light unto the nations. #noban — Marc Benioff (@Benioff) January 28, 2017

Facebook CEO Mark Zuckerberg

Zuckerberg was quick to lambast the immigrant ban in a Facebook post Friday.

Tesla CEO Elon Musk

Musk called the ban "not the best way to address the country's challenges."