El Salvador already has some of the most draconian anti-abortion laws in the world, but they could become even stricter if Congress adopts an opposition proposal to imprison women for up to 50 years if they terminate a pregnancy.

The Nationalist Republican Alliance (Arena) has submitted a motion to reform article 133 of the penal code, which stipulates the penalty for women who cause or consent to an abortion.

Existing sentences range from two to eight years – far higher than most countries, even in conservative Catholic Latin America – but the rightwing opposition wants to increase this from a minimum of 30 years to a maximum of 50 years. This is equivalent to the sentence in El Salvador for aggravated murder with “extreme cruelty”.

A copy of the document seen by the Guardian claims the reform is necessary to keep penalties in line with a constitution that guarantees the right to life, which is defined as beginning from the moment of conception.

It also calls for maximum penalties for causing “negligent injury to the unborn” to be raised from 100 days to two years, and for “sale of products that induce abortion” to increase from 30 days to three years.

Amnesty International called the proposals scandalous and irresponsible. “Parliamentarians in El Salvador are playing a very dangerous game with the lives of millions of women,” said Erika Guevara-Rosas, Americas director for the human rights group.

“Banning life-saving abortions in all circumstances is atrocious but seeking to raise jail terms for women who seek an abortion or those who provide support is simply despicable.”

The International Planned Parenthood Federation has also opposed the proposed increase in penalties, calling the move “shameful and irresponsible”.

“The proposal to increase the existing sentences for women who have had abortions is not only an egregious human rights violation; it flies in the face of evidence showing that restricting access to abortion does not reduce the number of abortions,” said Kelly Castagnaro, a spokeswoman for IPPF’s western hemisphere region.

Since 1998, abortion in El Salvador has been banned in all circumstances. Injustices are rife. Civil Rights groups say 17 women have been imprisoned for miscarriages or attempted terminations. In some cases, abortions are already treated as murder. Pregnant women who turn up at hospitals bleeding are sometimes handcuffed to the bed. Others are forced to go through births even when their lives are at risk, such as Beatriz, a 22-year-old woman who almost died because she was not permitted to terminate her pregnancy with a foetus that was missing large parts of its brain and skull.

In most countries, abortion is legal. In Europe, even murder is not treated as harshly. In the UK, 14 years is the average length of sentence served by people jailed for murder.