The mayor has been accused of ruining the atmosphere of Rio's famous Carnival with a zero tolerance approach to prostitution, drunkenness and debauched behaviour.

Eduardo Paes wants to end the Brazilian city's lawlessness with his Shock of Order campaign. But as this year's Carnival, billed as the world's biggest party, began on Friday, Paes was called a killjoy.

Those who drink too much beer at giant Carnival street parties and use gutters as toilets face a night in jail. To keep beaches clean, he has outlawed traditional Carnival foods on skewers, while beach football, a near religion in Brazil, is banned until 5pm.

The city's infamous waterfront pick-up club for legal prostitutes on Copacabana beach has been closed to make way for a museum.

Twitter users are fast becoming public enemy No. 1, at least in Mexico City, where they have angered authorities by warning one another of roadside alcoholimetro — or Breathalyzer — checkpoints set up by the police.

But the case against the Twitter is about more than alcohol. Mexico is, after all, a country at war — at least according to President Felipe Calderon, who launched the crackdown on drug cartels shortly after taking office. Three years later, the streets of border cities like Ciudad Juarez and Tijuana remain full of soldiers. In many ways, the government is still playing catch-up to the nation's criminals.

In this context, the issue of the Twitter has quickly expanded into an argument over whether public safety takes priority over free speech in a country struggling to contain serious social ills. Fearing that kidnappers and drug cartels use Twitter, Facebook or MySpace to communicate, the Mexican government is considering a bill to restrict social networking websites and to set up a police force to monitor them.

The Twitter feed in question, Anti Alcoholimetro, doesn't hide its intent. On any given night, a dozen people write in listing the time and location where they saw a police checkpoint, helping others to avoid it.

The government's response has been erratic. At first, city officials said tweeting the location of police checkpoints was a crime, akin to helping someone break the law, and vowed to find a way to prosecute Twitterers. But after a media frenzy, they quickly backed down.

Yet the right to tweet is far from guaranteed, even in the relatively liberal capital of Mexico City. Article 320 of the city's penal code prescribes prison terms of up to five years for those who in any way help a delinquent avoid investigation by the authorities or escape their actions.

If that seems vague, it is. But federal lawmakers are quickly working on specific legislation to track down and punish Twitterers who break the law or help others escape it.