Joe Biden is being urged to clarify a longstanding US law restricting overseas aid that has been misinterpreted by successive administrations as an outright ban on funding abortion for any reason. As the US president marked his first 100 days in office on Friday, more than 140 human rights and global health organisations, including Human Rights Watch, Amnesty International US and the Global Justice Center, signed a letter asking him to confirm that US aid can be used for abortion care in cases of rape, incest and when the woman’s life is in danger. The letter calls on the president to back a bill, introduced in Congress last year, to permanently repeal the 1973 Helms amendment, which has been wrongly interpreted as a ban on US money being used for abortion in any circumstances. The letter says: “As written, the law restricts the use of US foreign assistance for ‘abortion as a method of family planning’. This does not include cases of rape, incest, or life-endangerment; however, lack of clarity around the law has prevented the use of funds in these cases, even in humanitarian emergency settings.” The group want clear guidance issued on Helms and another misinterpreted law, the Leahy amendment. “The US is the largest funder of global health, including family planning, and is the only donor nation to single out abortion in this way,” the letter says. “Many US abortion restrictions, including the Helms amendment, have consistently been in place for decades, causing generations’ worth of harm – and they will continue to do so if action is not taken. This is a matter of utmost urgency as bodily autonomy and reproductive freedom are increasingly under siege.” During his first 10 days in office, Biden rescinded the Mexico City Policy – known as the “global gag rule” – which stopped overseas groups that received US aid using money from other sources to fund abortion services. Kamala Harris, the US vice-president, co-signed a bill to repeal the policy permanently – currently, it can be reintroduced or rescinded by each president. Akila Radhakrishnan, president of the Global Justice Center, said the belief that the Helms amendment banned abortion under all circumstances had become “normalised”. Bethany Van Kampen, an adviser at the signatory reproductive health charity Ipas, said the law “has to be fully repealed” but that in the meantime: “Why would we not mitigate the harm of Helms? That would save lives immediately.” The Guttmacher Institute, a pro-choice research organisation, has estimated that repealing the Helms amendment could result in 19m fewer unsafe abortions and 17,000 maternal deaths a year.