By Michael Christie

MIAMI (Reuters) - Greenpeace, charged with the obscure crime of "sailor mongering" that was last prosecuted 114 years ago, goes on trial on Monday in the first U.S. criminal prosecution of an advocacy group for civil disobedience.

The environmental group is accused of sailor mongering because it boarded a freighter in April 2002 that was carrying illegally felled Amazon mahogany to Miami. It says the prosecution is revenge for its criticism of the environmental policies of President Bush, whom it calls the "Toxic Texan."

Sailor mongering was rife in the 19th century when brothels sent prostitutes laden with booze onto ships as they made their way to harbor. The idea was to get the sailors so drunk they could be whisked to shore and held in bondage, and a law was passed against it in 1872. It has only been used in a court of law twice, the last time in 1890.

Greenpeace says the decision by the U.S. Attorney's Office to prosecute the organization rather than just the activists who boarded the APL Jade freighter is a sea change in policy, and a conviction would throttle free speech everywhere.

It would also be a sharp blow against Brazilian efforts to halt the trade in a hardwood so precious it is known as "green gold." It yields fatter profit margins than cocaine and is blamed for the destruction of vast swathes of the Amazon.

"Illegal logging goes on and they're bringing it to Miami and making loads of money, and we're going to trial," said Sara Holden of Greenpeace International.

The case is unprecedented, not just because of the bizarre nature of the crime.

Six Greenpeace activists were charged after the 2002 protest in choppy waters off Miami, pleaded guilty and sentenced to time served -- the weekend they spent in jail.

But U.S. prosecutors were not satisfied, and 15 months later came up with a grand jury indictment of the entire organization for sailor mongering.

FREE SPEECH CONCERNS

U.S. prosecutors argue Greenpeace did something like that when two "climbers" clambered aboard the Jade to hang a sign demanding, "President Bush: Stop Illegal Logging."

If convicted, Greenpeace could be placed on probation, and pay a $10,000 fine.

As significant as the prosecution itself, are the implications, free speech campaigners say.

Not once since the Boston Tea Party have U.S. authorities criminally prosecuted a group for political expression.

"It's ominous," said attorney Maria Kayanan of law firm Podhurst Orseck, which worked with the American Civil Liberties Union on a "friend of court" brief to back a Greenpeace demand that the government reveal who ordered the prosecution.

"It will be very chilling because advocacy groups whose members chose to engage in acts of protest which happen to violate the law will be loathe to act at all."

Greenpeace hopes to focus on mahogany during the trial, which will begin on Monday with jury selection in the U.S. District Court in Miami, under Judge Adalberto Jordan.

In one line of defense, its attorneys will argue that the activists were highlighting a crime, and giving Washington an opportunity to live up to its commitment to protect mahogany as a signatory to global treaties listing the wood as endangered.

Greenpeace Amazon campaigner Paulo Adario said a mahogany tree could be bought in the Amazon for $30. Once turned into dining tables and chairs for sale in New York or London, that same tree could be worth as much as $120,000.

Along the way, Amazon Indians are driven from their villages, officials bribed and activists assassinated.

Country-sized chunks of rain forest fall to chainsaws as other loggers take advantage of the roads the mahogany hunters carve to get at less valuable woods that would not otherwise have been worth trying to reach.

"Mahogany is a red wood, it's red like blood, it's red like shame," Adario said by phone from the Amazon port of Manaus. "The U.S. government should help us to change at least the shameful color of mahogany (but) they are prosecuting us."