A few prominent voices in Silicon Valley are calling for the tech world to exercise greater caution in vetting its investors as disquiet builds about one of the industry’s biggest backers -- Saudi Arabia -- and its role in the killing of journalist Jamal Khashoggi.

The calls, while still isolated, are challenging the hush-hush world of money-raising in the startup industry, where venture-capital firms and privately owned startups disclose little about their funding and operations.

“It is time for all of us in the startup and VC sector to do a deep dive on our investor base,” Fred Wilson, the influential founder of Union Square Ventures, a New York City-based venture capital firm with strong ties to the Valley, argued in a blog post Sunday. “Who are our investors and can we be proud of them?”

“It will be a real moral challenge for anyone to accept money moving forward from Saudi Arabia,” said Venky Ganesan, a partner at technology investor Menlo Ventures, which invested in Uber and Warby Parker, and former chairman of the National Venture Capital Association.

So far in public, the tech community is largely staying quiet -- reflecting the difficulty of undoing some investments and the traditionally discrete nature of the Valley’s many non-public companies and funds, industry experts say.

A clutch of startups that have received large sums from funds tied to Saudi Arabia, including the messaging app developer Slack and office-space provider WeWork, declined to comment for this article. More than a dozen other startups and venture-capital funds that have either received money from the kingdom, including Tesla and Magic Leap, or that are invested in companies alongside a Saudi-backed fund, such as Slow Ventures, didn’t respond to requests for comment.

The lack of broad public outrage stands in contrast to other political issues that Silicon Valley’s leaders and its employees have gotten involved in, such as the widespread protest of President Trump’s immigration policies and withdrawal from the Paris Climate Accord. But Silicon Valley tends to handle money matters in private: Venture capitalists and startups have also debated whether to take funds from Chinese investors but the conversation has not spilled into the open.

Silicon Valley “should be horrified by the Saudis’ barbarity, and the Khashoggi case is just the final straw,” said the region’s Democratic Congressman, Ro Khanna, pointing to Saudi Arabia’s involvement in a military campaign in Yemen that has killed thousands of civilians and pushed the country to the brink of famine, according to the United Nations. Khashoggi, a Saudi national, was a Washington Post contributor.

“People in the Valley really think of themselves as wanting to contribute to the furthering of Enlightenment ideals,” Khanna added. “This is such a slap in the face of those values.”

Several tech leaders including Uber’s CEO pulled their participation in a high-profile conference that Saudi Arabia’s sovereign-wealth fund is holding in Riyadh this week, nicknamed “Davos in the Desert.” Executives of other American companies appeared in the gilded halls of the King Abdul Aziz International Conference Center.

“Any CEO should be concerned if they have a murderer among their investors,” said Ali Partovi, CEO of Neo, a venture capital fund, and early investor in Facebook, Airbnb, Uber, Dropbox. “Your customers and employees are watching."

Saudi money has poured into U.S. startups from the kingdom’s Public Investment Fund. The kingdom is also the largest investor in the $93 billion SoftBank Vision Fund, which is the biggest fund ever raised in Silicon Valley. Saudi money makes up nearly half of it, alongside smaller investments from SoftBank Group, a Japanese conglomerate, as well as Apple, Qualcomm and others, according to the Vision Fund.

The Vision Fund declined to comment for this article. The Public Investment Fund didn’t respond to requests for comment.

In private, some in the tech industry are now criticizing the Saudi influence. Venture capitalists said that their firms have cancelled upcoming meetings with Saudi investors. One prominent venture capital firm in the Valley said that an email chain was circulating within the firm about whether to take new money from Saudi investors, saying that the money had been perceived as “clean” until the Khashoggi incident. Venture capital firms are not required to disclose their investors, and such details are often closely held.

Wilson of Union Square Ventures wrote that he received an email last week from the CEO of a company in which his firm had invested. The executive wanted to know whether Union Square had received money from certain bad actors. The CEO was asking “because questions were coming up internally and he wanted to answer honestly and accurately,” Wilson wrote, adding that he didn’t recall ever getting the question before.

Wilson and others said many investment relationships, even if now regretted, will be hard to unwind.

It is extremely difficult to return money in Silicon Valley, Ganesan said. For one, there aren’t legal mechanisms to force any investor to return shares they have already purchased, he said. In addition, the valuation of startups is determined by the investors who contribute money during each round of funding. Even if the company hasn’t already spent the funds, the exit of a large investor would likely upend the share price and the company’s valuation, causing confusion and possibly legal ramifications among other investors and employees who are compensated through stock options.

When the kingdom’s sovereign-wealth fund invested $3.5 billion in Uber in 2016 and gained a board seat at the ride-hailing company, it was the largest single investment ever made in a privately-held company at the time. The investment in the transportation company stoked controversy at the time because Saudi Arabia banned women from driving. (The ban has since been lifted.) The Saudis gained more control of Uber when SoftBank Vision Fund invested another $7.7 billion in the startup in 2017.

In an Oct. 11 statement, Uber chief executive Dara Khosrowshahi said he was “very troubled” by the reports about Khashoggi. Uber declined to comment further.

Much of Saudi Arabia’s investment has flowed to tech startups through the SoftBank Vision Fund, founded two years ago. SoftBank Group and its chief executive, Masayoshi Son, helped the Saudis gain acceptance among startups that might have felt squeamish taking money directly from Riyadh, tech executives say. “A Japanese firm feels safer to most firms than a Saudi Arabian investment vehicle,” says Bob Kocher, a partner at venture-capital firm Venrock, which is known for its early investments in Apple, AthenaHealth and Dollar Shave Club.

Yasir Al Rumayyan, managing director of Saudi Arabia’s sovereign wealth fund and the Uber board member, last year said the kingdom hoped its Vision Fund investment would bring dividends at home, supporting the country’s goal of developing a “diversified, knowledge-based economy.”

Saudi Arabian Crown Prince Mohammed bin Salman made a much-publicized trip to the Bay Area in June 2016, when he was still deputy crown prince, meeting with Facebook co-founder Mark Zuckerberg and trying on an Oculus virtual-reality headset.

He returned to the West Coast this year, getting a tour of Google’s campus with co-founder Sergey Brin and holding additional meetings with Amazon founder Jeff Bezos and Apple CEO Tim Cook. (Bezos is the owner of The Washington Post.) The crown prince traveled with a female former Microsoft vice president in Saudi Arabia, and together they made the case for women in innovation. (He famously rented out the entire 200-room Four Seasons hotel in Palo Alto for five nights, according to reports.)

The Vision Fund quickly became the most aggressive investor in the startup world. Its billions supported the driverless car developer GM Cruise, the real-estate companies Opendoor and Compass and the food-delivery business DoorDash. The dog-walking startup Wag Labs Inc. had raised about $60 million from various investors between 2015 and 2018 -- until the Vision Fund came along early this year and gave it $300 million, according to data provider PitchBook. “Why Does Wag Need $300M From SoftBank To Walk Dogs?” asked a headline on Crunchbase News, an industry publication.

Officials from Wag Labs, GM Cruise, Opendoor and DoorDash didn’t respond to requests for comment.

That eagerness to put up so much cash has upset the power dynamics in Silicon Valley, because the Vision Fund is effectively able to beat out many other investors, who have criticized it for using hardball tactics to get in on deals. But SoftBank Vision Fund, with its Saudi backers, has also provided much-needed liquidity to mature startups worth tens of billions of dollars that have delayed going public.

Robert Reffkin, CEO of Compass, said: "SoftBank has been a great partner to us and we look forward to continuing to grow with them. Of course, the death of Jamal Khashoggi is beyond disturbing because the freedom and safety of the press is something that is incredibly important to me."

At an investment conference in Riyadh several months after the Vision Fund’s launch last year, Son and Saudi Crown Prince bin Salman shared a stage with journalist Maria Bartiromo, Blackstone Group CEO Stephen Schwarzman and others, where they discussed the kingdom’s modernization plans.

The conference this year, which began Tuesday, is mired in controversy. Colleagues and friends of Uber’s Khosrowshahi applauded him for being one of the first to drop out of the event, according to people familiar with the conversations. Uber board member Arianna Huffington joined him in abstaining.

Softbank founder Son and Softbank Chief Operating Officer Marcelo Claure also dropped out, according to a person familiar with the matter, a sign of potential tension between Saudi Arabia and Softbank.

However, others are still attending, including Saleh Romeih, a managing partner at Softbank Vision Fund, who spoke on a panel Tuesday, the person said.

Cat Zakrzewski and David J. Lynch contributed to this article.

Editor’s note: An earlier version of this story included Slow Ventures in a group of companies that have received money from Saudi Arabia or invested alongside it. Slow Ventures, which didn’t respond to requests for comment before publication, on Wednesday said it has not to its knowledge received money from Saudi Arabia. Slow Ventures added that it invested in a Silicon Valley startup, Wag Labs, before the Saudi-backed SoftBank Vision Fund did. Both funds are currently shareholders in Wag Labs.