Environmental group Greenpeace is going on trial in the US under an archaic law last enforced 114 years ago.
The charges arise from a protest over illegal logging
The group was charged with "sailor-mongering" after its activists boarded a ship in April 2002 that was carrying illegally-felled Amazon mahogany.
It is thought to be the first US criminal prosecution of a pressure group for civil disobedience.
Greenpeace says the case is revenge for its criticism of President George W Bush's environmental policies.
In a statement on its website, Greenpeace says the prosecution "poses a serious threat to citizens' right to free speech and to engage in peaceful dissent".
The rarely-used law dates from 1872 and was originally aimed at preventing boarding-houses from luring sailors away from their ships with offers of prostitutes, strong drink and warm beds.
Legal texts mention the law only twice, most recently in 1890.
"Never has anything like this been done and it's particularly suspect in light of the mission of
Greenpeace," said Maria Kayanan, a lawyer with the American Civil Liberties Union who is helping in Greenpeace's defence.
In a tactic the group has often used to make a point, the activists attempted to unfurl a large banner on the ship to protest what they saw as the Bush administration's inaction on a ban on Amazon mahogany imports.
Individual Greenpeace members were prosecuted immediately.
In an unprecedented move, prosecutors indicted the organisation itself 15 months later on misdemeanour charges of illegal boarding and conspiracy.
A conviction could be punished by five years of probation and a $20,000 fine.
US District Judge Adalberto Jordan has rejected Greenpeace's attempts to access records to find out who authorised the prosecution.
Prosecutors have not spoken publicly about the case outside the courtroom.