In the history of political upheavals, communication is in many ways the most powerful tool available to both entrenched power and upstart. However control over those communications tends to lie firmly in the hands of the former. Case in point: According to reports across the Internet, for the last several days, the Egyptian government has been blocking access from within its borders to social networks, namely Twitter and Facebook.

Over the last two days, roughly 20,000 Egyptian protesters, inspired by the recent Tunisian demonstrations against government corruption, have marched for an end to the 30-year-old dictatorship of 82-year-old President Hosni Mubarak in cities including Alexandria, Suez, and North Sinai. The protestors hold Mubarak’s regime largely responsible for the country’s poverty, high food prices, government corruption and mismanagement.

“Down with Hosni Mubarak, down with the tyrant,” they reportedly chanted. “We don’t want you.”

Many of the protestors were met with riot control measures like tear gas and water canons: 860 citizens have been arrested so far and at least three were killed on both sides of the demonstrations: Two demonstrators were fatally wounded by rubber bullets and one policeman was struck in the head.

As part of its strategy to quash the protests, the government blocked local access first to Twitter, then Facebook hours later, where to some extent, the protests were organized beforehand.

“We can confirm that Twitter was blocked in Egypt around 8 a.m. PT today,” the company tweeted from the handle @twitterglobalpr. “It is impacting both Twitter.com @applications. … We believe that the open exchange of info & views benefits societies & helps govts better connect w/ their people.”

The Facebook block disallowed Egyptian users from viewing demands that called for, among other things, Mubarak and Prime Minister Ahmed Nazif’s resignations, the dissolution of the country’s parliament, and the subsequent creation of a new government. The block also affected access to pages like “We are all Khaled Said,” inspired by the death of an Egyptian reportedly tortured and killed by police an Alexandria. Reported by TechCrunch as a major contributor to the online mobilization of the protests, the page has 18,200-plus fans and features continuous updates with photos and videos. (In fact, as of publication, the page reported that local mobile carrier Vodafone Egypt had allegedly been ordered by the government to also block Gmail, Google chat (GOOG), and access to other unspecified sites.)

In many ways, the situation resembles the events in Iran leading up to the 2009 presidential elections. Candidates then opposing current, controversial President Mahmoud Ahmadinejad used social networks as part of their campaigns, to organize events, attract supporters, and distribute information to them. At one point Twitter, at the request of the U.S. Department of State, even postponed a planned service outage to insure Iranians could continue to communicate using the service. Then, without warning, the Iranian government stepped in and blocked social network access.

Egypt appears to have learned from Iran’s experience, blocking social media access far more quickly, relative to Iran, in the cycle of unrest. In Egypt’s case, the question has become: how will social networks respond to an issue that threatens to stifle global growth?

Though Twitter did not respond in time for comment, Facebook was directing media inquiries to the website Herdict, which aggregates website access reports from around the world. Worth noting is that the blocking of Twitter.com may not mean Twitter in Egypt is unusable: Harvard Professor of Computer Science and Law Jonathan Zittrain argued in a post back in 2009 that Twitter’s unique infrastructure, which allows multiple data paths in and out to various web sites and third party applications, makes it naturally more “censorship resistant.” In other words, Twitter.com may be blocked in countries like Egypt (and Iran), but it may be possible for outside sites and services to access and display tweets to locals, and to allow locals to post to the service.

That’s probably of little comfort to Egypt’s social media-savvy users who, like Tunisia and Iran’s citizens before them, face an unsettling message: Disagree with the ruling powers and some basic freedoms will soon be wrenched away.