Thursday's announcement that Twitter had refined its technology to censor messages on a country-by-country basis raised fears that the company's commitment to free speech may be weakening. Twitter is trying to broaden its audience and make more money by expanding around the globe.
"I'm afraid it's a slippery slope of censorship," said social media commentator Jeff Jarvis, interviewed at a gathering of business and government leaders in Davos, Switzerland.
"I understand why Twitter is doing this -- they want to be able to enter more countries and deal with the local laws. But, as Google learned in China, when you become the agent of the censor, there are problems there," he added.
Egyptian activist Mahmoud Salem, who tweets and blogs under the name "Sandmonkey," questioned in a tweet whether Twitter "is selling us out."
Twitter sees the censorship tool as a way to ensure individual messages, or tweets, remain available to as many people as possible while it navigates a gauntlet of different laws around the world.
Before, when Twitter erased a tweet it disappeared throughout the world. Now, a tweet containing content breaking a law in one country can be taken down there and still be seen elsewhere.
Twitter will post a censorship notice whenever a tweet is removed. That's similar to what Internet search leader Google Inc. has been doing for years when a law in a country where its service operates requires a search result to be removed.
Like Google, Twitter also plans to the share the removal requests it receives from governments, companies and individuals at the chillingeffects.org website.
The similarity to Google's policy isn't coincidental. Twitter's general counsel is Alexander Macgillivray, who helped Google draw up its censorship policies while he was working at that company.
"One of our core values as a company is to defend and respect each user's voice," Twitter wrote in a blog post. "We try to keep content up wherever and whenever we can, and we will be transparent with users when we can't. The tweets must continue to flow."
Twitter, which is based in San Francisco, is tweaking its approach now that its nearly 6-year-old service has established itself as one of the world's most powerful megaphones. Daisy chains of tweets already have played instrumental roles in political protests throughout the world, including the Occupy Wall Street movement in the United States and the Arab Spring uprisings in Egypt, Bahrain, Tunisia and Syria.
It's a role that Twitter has embraced, but the company came up with the new filtering technology in recognition that it will likely be forced to censor more tweets as it pursues an ambitious agenda. Among other things, Twitter wants to expand its audience from about 100 million active users now to more than 1 billion.
Reaching that goal will require expanding into more countries, which will mean Twitter will be more likely to have to submit to laws that run counter to the free-expression protections guaranteed under the First Amendment in the U.S.
If Twitter defies a law in a country where it has employees, those people could be arrested. That's one reason Twitter is unlikely to try to enter China, where its service is currently blocked. Google for several years agreed to censor its search results in China to gain better access to the country's vast population, but stopped that practice two years after engaging in a high-profile showdown with Chain's government. Google now routes its Chinese search results through Hong Kong, where the censorship rules are less restrictive.
In China, where activists quickly caught on to Twitter despite it being blocked inside the country, artist and activist Ai Weiwei tweeted Friday: "If Twitter censors, I'll stop tweeting."
China's Communist Party remains highly sensitive to any organized challenge to its rule and responded sharply to the Arab Spring, cracking down last year after calls for a "Jasmine Revolution" in China.
Many Chinese find ways around the so-called "Great Firewall" that has blocked social networking sites such as Twitter and Facebook.
Nelson Bocaranda, a Venezuelan journalist, radio host and outspoken opponent of President Hugo Chavez, warned that Twitter's decision could prompt a government crackdown on critics' tweets ahead of the Oct. 7 presidential election.
"Twitter has become a weapon to preserve our embattled democracy," said Bocaranda, who has more than 482,000 followers.
Twitter is "an important tool" for Venezuelans to share information as local media resort to self-censorship as means of avoiding conflict with government officials, Bocaranda added.
Salem, the Egyptian activist, added in a tweet on his account: "This is very bad news."
"Is it safe to say that (hash)Twitter is selling us out?" he wrote.
"Clearly there is a huge user backlash against this latest move by Twitter," said blogger Mike Butcher, editor of Tech Crunch Europe.
"It was seen as one of the few platforms that was free of any kind of censorship, heavily used during for example Arab spring and even in Russia lately over protests over the elections. It is, to some extent, something that we could have predicted," Butcher said.
In its Thursday blog post, Twitter said it hadn't yet used its ability to wipe out tweets in an individual country. All the tweets it has previously censored were wiped out throughout the world. Most of those included links to child pornography.
Google Executive Chairman Eric Schmidt declined to comment on Twitter's action and instead limited his comments to his own company.
"I can assure you we will apply our universally tough principles against censorship on all Google products," he told reporters in Davos.
Google's chief legal officer, David Drummond, said it was a matter of trying to adhere to different local laws.
"I think what they (Twitter officials) are wrestling with is what all of us wrestle with -- and everyone wants to focus on China, but it is actually a global issue -- which is laws in these different countries vary," Drummond said.
"Americans tend to think copyright is a real bad problem, so we have to regulate that on the Internet. In France and Germany, they care about Nazis' issues and so forth," he added. "In China, there are other issues that we call censorship. And so how you respect all the laws or follow all the laws to the extent you think they should be followed while still allowing people to get the content elsewhere?"
Associated Press writers Christopher Toothaker in Caracas, Venezuela, Angela Charlton in Davos, Switzerland, Cara Anna in New York and Ben Hubbard in Cairo contributed to this story.