Rob Rhinehart, a co-founder of nutritional drink start-up Soylent, declared in a blog post last week that he was supporting Kanye West for president.

“I am so sick of politics,” Mr. Rhinehart wrote. “Politics are suddenly everywhere. I cannot avoid them.”

David Barrett, the chief executive of Expensify, a business software start-up, went in another direction. In an email to his company’s 10 million customers last week, he implored them to embrace politics by choosing the Democratic presidential nominee, Joseph R. Biden Jr.

“Anything less than a vote for Biden is a vote against democracy,” Mr. Barrett proclaimed.

With days to go before the election on Tuesday, Mr. Rhinehart and Mr. Barrett represent the twin poles of a start-up culture war that has openly erupted in Silicon Valley. Start-ups such as the cryptocurrency company Coinbase and the audio app Clubhouse have become embroiled in a debate over how much politics should be part of the workplace. And venture capitalists and other tech executives have weighed in on social media with their own views.

“I have never seen another instance like this in my career,” said Bradley Tusk, a venture capitalist and political consultant. “There’s no real separation anymore, in the current political climate, between politics and everything else. It has permeated absolutely everything.”

Silicon Valley tech workers have long been regarded as liberal but not politically overactive. After President Trump’s victory in 2016, however, workers at large tech companies such as Google and Amazon began agitating more on issues like the ethics of artificial intelligence, immigration and climate change.

Now many start-up workers, who have been sold on a mission of changing the world, expect their employers to support their social and political causes, entrepreneurs and investors said. This summer’s protests against police violence prompted many tech companies to re-examine their own issues with race. And the pressure to make political moves before the election has only intensified.

The shift has grown partly out of a realization that no tech platform is completely neutral, said Katie Jacobs Stanton, who invests in start-ups through her venture capital firm, Moxxie Ventures. Founders who build companies with millions of users “really have an obligation to have a point of view and make sure their products are being used for good,” Ms. Stanton said.

“It’s disingenuous and it’s also the luxury of the privileged to say, ‘We don’t have a point of view,’” she added.

But others said they feared becoming a lightning rod or inflaming tensions at a hypersensitive moment during the coronavirus pandemic. Some worried that their companies could be sued by employees who might say they were discriminated against because of their political beliefs. Others said any move could be attacked by those who found the actions inauthentic or not enough.

Those tensions exploded in public last month when Brian Armstrong, the chief executive of Coinbase, penned a 2,000-word blog post to “clarify” his company’s culture. Mr. Armstrong wrote that he wanted Coinbase to generally avoid engaging with broader social issues and workplace conversations about politics. He said it was a way to minimize distraction and focus on the start-up’s mission of creating “an open financial system for the world.”

Two months earlier, dozens of Coinbase employees had staged a walkout after executives were slow to express solidarity with Black Lives Matter protesters and minority employees, several workers said. In his post, Mr. Armstrong said employees who disagreed with his “no politics” stance could leave.

His position immediately created waves across Silicon Valley. Some praised the move, with one Coinbase investor comparing Mr. Armstrong to Michael “Jordan in his prime.” Others said opting out of politics was itself a political statement.

Dick Costolo, a former chief executive of Twitter, tweeted that “me-first capitalists who think you can separate society from business” would be shot in “the revolution.” He deleted the post after, he said, it set off violent threats and harassment.

In an interview, Mr. Costolo said it was impossible for companies to separate their mission from their impact on the world. “If you try to separate the social contract from the economic contract, don’t be surprised when there’s an uprising, because they’re linked,” he said.

Some Coinbase workers disagreed with Mr. Armstrong. “I’m just so mystified by the apparent lack of awareness in the blog post,” Ryan King, a Coinbase engineer, wrote on the company’s internal Slack messaging system. The message was reviewed by The New York Times. “A declaration that we’re not going to touch ‘broader societal issues’ fails to acknowledge that we’re a part of society,”

About 60 Coinbase employees, or 5 percent of the work force, have resigned, the company said. A spokeswoman declined further comment.

Fred Wilson, an investor at Union Square Ventures and a Coinbase board member, said in an interview that there were no easy answers for start-up leaders. “Many, many C.E.O.s have told me privately that they would like to have done what Brian did but don’t want to take the heat that he has taken,” he said.

On Monday, Mr. Wilson wrote a blog post about removing start-up chief executives who have “failed to manage numerous important challenges.” The post prompted speculation that he was referring to Mr. Armstrong, but Mr. Wilson said it was a metaphor for President Trump.

The political debates among Silicon Valley start-ups have ramped up since the Coinbase episode. Last week, Soylent’s Mr. Rhinehart published his post supporting Mr. West’s presidential bid. Mr. Rhinehart, who is on the board but not involved in the company’s day-to-day operations, also attacked the political system and the media, writing that “politics has always been based on jokes.”

Demir Vangelov, Soylent’s chief executive, said Mr. Rhinehart’s post did not represent the company. Soylent’s focus is on bringing “the best complete nutrition to everyone,” he said, and it does not take political stances.

At Expensify, based in Portland, Ore., Mr. Barrett took a different position. After spending more than a decade in Silicon Valley, where he found a “uniform view” that politics was not good for business, he moved to Portland four years ago. Now, he said, “choosing not to participate is also a choice — it’s a choice to defend the status quo.”

So when Expensify employees drafted an email to tell customers to vote for Mr. Biden, after concluding in an internal discussion that re-electing Mr. Trump would be a threat to democracy, Mr. Barrett favored sending it out. While roughly a third of Expensify’s top management opposed sending the email because it could alienate customers, the majority ruled, Mr. Barrett said.

Last Thursday, Expensify blasted its message to its 10 million users. “Not many expense reports get filed during a civil war,” Mr. Barrett wrote.

The email instantly drew criticism and praise on social media. Job applications, web traffic and customer sign-ups have since spiked, Mr. Barrett said. But he also received death threats, prompting him to hire private security. No customers have quit, potentially because Expensify’s system takes months to switch out of, he said.

Tayo Oviosu, chief executive of Paga, a payments start-up in Lagos, Nigeria, said Expensify’s email had crossed a line. Mr. Oviosu isn’t opposed to companies’ speaking up on social justice issues, “but that is very different than leveraging the fact that you used my personal information to tell me I have to vote in a certain way,” he said. “That is wrong.”

Mr. Oviosu, who was using a trial version of Expensify and was considering adopting the paid version, said he now planned to look at alternatives. “I think they lost me completely on this,” he said.

The start-up culture wars are also evident on Clubhouse, where people join rooms and chat with one another. The app has been a popular place for investors such as Marc Andreessen and other techies to hang out in the pandemic. (Mr. Andreessen’s venture firm, Andreessen Horowitz, has invested in Clubhouse, Coinbase and Soylent.)

On Oct. 6, Mr. Andreessen started a Clubhouse room called “Holding Space for Karens,” which describes having empathy for “Karens,” a slang term for a pushy privileged woman. Another group, “Holding Space for Marc Andreeeeeeeeeeeeeeeessen,” soon popped up. There, people discussed their disappointment with the Karen discussion and other instances when, they said, Clubhouse was hostile to people of color.

Mr. Andreessen and others later started a Clubhouse room called “Silence,” where no one spoke. Andreessen Horowitz declined to comment.

At a “town hall” inside the app on Sunday, Clubhouse’s founders, Paul Davison and Rohan Seth, were asked about Coinbase’s and Expensify’s political statements and where Clubhouse stood. They said the company was still deciding how Clubhouse would publicly back social causes and felt the platform should allow for multiple points of view, a spokeswoman said. She declined to comment further.

Yet even those wishing to stay out of politics are finding it hard to avoid. On Saturday, Mr. Armstrong shared Mr. Rhinehart’s blog post endorsing Mr. West on Twitter. “Epic,” tweeted Mr. Armstrong.

Several users pointed out the hypocrisy in Mr. Armstrong’s sharing something political after telling employees to abstain. One of his employees, Jesse Pollak, wrote that Mr. Armstrong had shared something with “a large number of inaccuracies, conspiracy theories, and misplaced assumptions.”

Soon after, Mr. Pollak and Mr. Armstrong deleted their tweets.