Amnesty's highly unusual step reflects international outrage about the case of the so-called Bolton Seven. The human rights organisation rarely adopts prisoners-of-conscience in this country, and there are none in British jails at present.
The men were convicted last month of offences including buggery and gross indecency after police seized video tapes on which they had recorded themselves. Sex between men is illegal if more than two people are present.
The parties took place at the home of one of the defendants, Norman Williams. All the men were over the age of consent, except one, who was six months short of 18. All, including the youngest, were willing participants.
The Bolton case has become a cause celebre in the gay community, and the men have received more than 400 letters of support from individuals and human rights groups around the world, including Australia, South Africa and Romania.
An Early Day Motion has been tabled by the Liberal Democrat MP Dr Evan Harris, who asked the Attorney-General a question in the Commons yesterday about issues relating to the case.
The Bishop of Edinburgh, the Most Rev Richard Holloway, is among eminent figures who have written to the judge, Michael Lever QC, urging him to "dispense justice with mercy".
The offences carry prison sentences of up to five years, and the judge has warned that he is inclined to jail at least some of the seven. Williams, 33, and, Terry Connell, 55, are regarded as most vulnerable because they were filmed with the 17-year-old, who cannot be named.
However, campaigners point out that the higher age of consent for gay sex has already been declared a breach of human rights by the European Commission, and that Westminster will almost certainly vote to lower it to 16 later this year.
The 17-year-old, who has been convicted of gross indecency despite his legal status as a minor, has submitted a statement to be used in mitigation today. In it, he says: "No one seduced me or pressed me to do anything against my will. I hope the judge will recognise that our relationships were harmless."
Sources close to the case say that police originally raided Williams' house in the mistaken belief that he was part of a paedophile ring.
It has also emerged that Dame Barbara Mills, the Director of Public Prosecutions, endorsed the decision to prosecute the men. In a letter to Brian Iddon, MP for Bolton South-East, Dame Barbara insisted that the prosecution was in the public interest.
Amnesty yesterday called on the Government to amend laws that penalise gay men for private, consensual sexual conduct. Soraya Bermejo, a spokeswoman, said: "The law as it stands constitutes a violation of human rights."