Famed for its human rights work, Amnesty International is under siege from religious groups outraged by a proposal that would expand Amnesty's mandate to include supporting access to abortion in cases such as sexual violence.

A small but growing band of anti-abortion campaigners and Roman Catholic clerics — including some who have backed Amnesty's activities in the past — claim the Nobel Prize-winning group is drifting away from its principles of unbiased advocacy.

They have threatened to pull away members and donations, and have called for a flood of protest letters to Amnesty offices — the same strategy Amnesty uses to pressure for the release of political prisoners and others.

Amnesty officials note that any decision is still more than a year away at the earliest, and defend their right to debate abortion and birth control within the context of women's rights.

Top Amnesty officials were unavailable for interviews, but the group released a statement from its London headquarters saying the group "does not make policy according to the ebbs and flows of external pressure."

It's unclear how deeply the anti-abortion factions could punish Amnesty. But religious groups have long been a pillar of the organization, which was founded in 1961 by a Catholic lawyer in Britain and now has more than 1.8 million members and many other supporters around the world. Its work to free people held by repressive regimes led to Amnesty winning the 1977 Nobel Peace Prize.

"This is completely inconsistent with what Amnesty has been about," said John-Henry Westen, a board member of the Campaign Life Coalition, a Toronto-based group representing about 110,000 families. "We consider this an attack on the rights of the unborn."

Westen said some members — including several "significant" financial contributors to Amnesty — already have stopped supporting the group.

"This is forcing people to make a choice," he said.

Amnesty's various regional offices are being asked to study whether to end the group's official "neutral" stance on abortion. In its place, the group could declare access to abortion a human right in specific cases including rape and life-threatening pregnancy complications. The proposals — growing out of Amnesty's campaign to stop violence against women — also include whether to support legal access to contraception.

Few places, including the United States, appear ready for an up or down vote on the matter. Instead, the discussions so far have been general, noncommittal and passionate. In New Zealand, Amnesty's local director, Ced Simpson, said there have been "strongly held views on both sides of the debate."

A final decision could come at Amnesty's next international gathering — in Mexico in August 2007. But the Amnesty statement said "much depends on the outcomes" of the current debates in various countries. If there's agreement that the abortion rights proposal has support, it could either be adopted by consensus or put to a formal vote. Otherwise, it could be dropped or sent back for more discussions.

In the meantime, opponents are trying to ignite a global movement that would draw in conservative Muslims and evangelical churches. Their long-range worry is that Amnesty's move could encourage other rights and aid agencies to take similar views on abortion and birth control. Last year, a statement from Medecines Sans Frontieres, or Doctors Without Borders, said its field workers can consider all measures, including abortion, when treating victims of sexual violence.

"We are deeply disappointed by the path taken by Amnesty. For those of us who champion real human rights, these trends makes us a bit queasy," said Austin Ruse, the Washington-based president of the Catholic Family and Human Rights Institute, a nonprofit research group that has called its 100,000 members to mobilize against the proposal.

In Britain, one of the largest anti-abortion groups, the Society for the Protection of the Unborn Child, has urged its members to turn their backs on Amnesty if the proposal is passed.

"You can't just support a group because they do some good things," said Janet Thomas, a society member in Wales. "You have to weigh your decision against the bad things they do."

Pope Benedict XVI has not spoken on the issue. But some high-ranking clerics have denounced the proposal, including Cardinal Renato Martino, head of the Vatican's office for peace and justice.

An open letter by Bishop Michael Evans of East Anglia, England — a 30-year member of Amnesty — said it would be "very difficult for Catholics and many others" to continue supporting Amnesty if the proposal is passed. In Canada, Bishop Frederick Henry of Calgary called the proposal "a gross betrayal" of Amnesty's mission and policies, which including opposition to the death penalty.

Amnesty says the discussions under way include broader issues such as the health risks of illegal abortions and forced marriages of young girls.

Amnesty's policy positions, the group said in its statement, "are rooted in human rights values, principles and standards and not in public and popular opinion."