Twitter announced Thursday that it has technology in place to selectively block tweets in specific countries.

Previously, if a government anywhere in the world made a legitimate request to block a tweet, Twitter had to block that tweet around the world. "Starting today, we give ourselves the ability to reactively withhold content from users in a specific country—while keeping it available in the rest of the world," Twitter said in a company blog.

"We haven’t yet used this ability, but if and when we are required to withhold a Tweet in a specific country, we will attempt to let the user know, and we will clearly mark when the content has been withheld," it continued.

The obvious question here is what Twitter will do when freedom fighters, like those who participated in the Arab Spring last year, tweet their dissent or use the service to organize protests. Will Twitter agree if a repressive government wants to silence their own people?

Twitter thinks that's an unlikely scenario, according to Danny Sullivan, writing in Marketing Land. Authoritarian governments usually either ignore Twitter or shut down the entire service, the company says. They don't ask to censor specific tweets.

When Twitter blocks content, it will post a notice of its action to Chilling Effects, an online rights joint project of the Electronic Frontier Foundation and the law schools at Harvard, Stanford, Berkeley, University of San Francisco, University of Maine and George Washington University, and the Santa Clara University School of Law.

Twitter's Chilling Effects page currently shows that the company has blocked a number of tweets because they include alleged violations of the Digital Millennial Copyright Act (DMCA).

Twitter explained in its help center that the ability to block tweets was necessary for the service to expand around the world. "If we receive a valid and properly scoped request from an authorized entity, it may be necessary to reactively withhold access to certain content in a particular country from time to time," it said.

Despite its new ability to censor, Twitter maintains its commitment to free expression is as strong as ever. "One of our core values as a company is to defend and respect each user’s voice," it said in its blog. "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."

Follow freelance technology writer John P. Mello Jr. and Today@PCWorld on Twitter.