Venezuela on Tuesday asked Twitter to block the accounts of users who are posting the unofficial dollar exchange rate -- illegal in a country that has had strict currency controls since 2003. The state telecom regulator Conatel sent an "urgent" letter to Twitter headquarters in San Francisco, California, asking them to "block the accounts and users of its web site which illegally listed currency in Venezuela," the agency explained on its web site. According to Venezuelan law, it is illegal to publish the black market exchange rate, which is eight times higher than the official rate of 6.3 bolivars per dollar. The government argues doing so encourages speculation and accelerates inflation. The agency wrote that publishing the black market rate for dollars on Twitter is "highly burdensome for the Venezuelan economy and potentially harmful for the Internet service providers that do not block the content." The US company did not immediately respond to a request for comment. Conatel's request seeks to block the 50 web sites closed November 9 by the government from taking to Twitter to circumvent the official ruling. The sites, although illegal, had existed for several years and published the unofficial exchange rate -- and if they were shut down, they would quickly reappear under different names. The only official way to obtain dollars in Venezuela is through the so-called currency management agency (Cadivi), which sells them at 6.3 bolivars to the dollar, or through auctions organized by the central bank, in which dollars can go for 10 to 12 bolivars for a dollar.