A group of 18 prominent scientists—including some who helped develop CRISPR–Cas9, the current leading tool for gene editing—issued a call Wednesday for an international moratorium on gene edits to eggs, sperm or embryos, and for establishing a process to discuss how and whether it should ever occur again.

The move follows Chinese scientist He Jiankui’s announcement late last year that he had edited the genes of twin newborn girls, in attempt to make them genetically resistant to HIV. This was CRISPR’s first known use in human embryos destined for life. There had been a general global consensus to hold off on editing human eggs, sperm or embryos until gene-editing technology (and the implications of the edits) are better understood. But He’s decision to proceed—and some scientists’ focus on gaining regulatory approval rather than achieving societal consensus—showed clearer lines have to be drawn, says commentary co-author Eric Lander, president and founding director of the Broad Institute of MIT and Harvard, a genetics research institute.

Lander says the group is calling for a temporary moratorium as a first step. What the scientists ultimately want to see is a global mechanism for discussing whether, and under what circumstances, people should be allowed to make gene edits that will be transmitted across generations.

The commentary, set to be published this week in Nature, suggests each country could set its own rules—but an international governance framework would ensure public discussion take place before decisions are made. One possible governing body could be a new committee that has been set up by the World Health Organization, scheduled to meet for the first time on March 19. Nature is also publishing an editorial supporting the commentary, as well as two approving letters: one from the heads of the U.S. National Academy of Medicine, the National Academy of Sciences, and the Royal Society in London; the other from the director of the U.S. National Institutes of Health and a colleague.

Victor Dzau, president of the National Academy of Medicine and a co-signer to one of the letters, says he fully supports the commentary’s proposals, and that he and his colleagues had already been pursuing similar objectives. “We are responding to their call. We are absolutely working on it,” he says. Dzau and his counterparts at the National Academy of Medicine and the Royal Society are jointly preparing a report, set for release later this year, that digs into the scientific and regulatory issues around editing genes that are inherited. There is no question, he says, that eggs, sperm or embryos should not be gene-edited until the implications and consequences are fully understood—if ever. Surveys clearly show much of the public is not ready to accept the idea of so-called designer babies, he says, although some people might support gene editing to enable the birth of a healthy child to parents who would otherwise pass down a serious genetic disorder.

The commentary’s authors make a clear distinction between germ-line editing—which is performed on embryos, eggs or sperm, and is passed to descendants—and somatic cell edits, which aim to address inherited diseases in children or adults and do not become embedded in the human gene pool. Most of the scientific community strongly supports editing somatic cells to treat diseases including sickle cell anemia, Huntington’s disease and Duchenne muscular dystrophy.

But there is far less agreement on whether altering humanity’s genetic inheritance should be allowed. Some worry such genetic enhancement would lead to attempts at designer babies—“remaking the human species based on your idea of what’s the best way to make a human being,” as Lander puts it. “I’m deeply skeptical about these enhancement applications,” he says. “I think at the moment it would be hubris—because we know so little—to consider such things. And even if we learn more, it might be deeply problematic.” But Lander says he can see an argument for allowing germ-line gene edits in the case of parents who want biological children but would otherwise unavoidably pass on an inherited disease.

Jane Maienschein, a historian of science at Arizona State University, says she would like to see the scientific community keep open the option to someday edit the human germ line. She notes there may be a future scenario, such as a disease epidemic like AIDS, for which there is no other treatment or cure besides germ-line editing. “It’s not thinking about what we need now, but it’s thinking ahead,” she says. “What is the next thing?”

In contrast, Marcy Darnovsky, who heads an advocacy organization called the Center for Genetics and Society, favors a permanent prohibition. She says germ-line editing is “not safe, it’s not needed and it’s way too dangerous from a social point of view.” She supports the goals of the coalition’s commentary, and hopes an open and fair global discussion will bring more people around to her point of view.

Harvard Medical School geneticist George Church, who has also been at the forefront of gene editing, says laws in place in the U.S., China and elsewhere already restrict gene editing more than would the voluntary system called for in the commentary. If the community wants to stop or limit germ-line editing, it should set up a stronger system of “carrots and sticks” that would motivate the scientific community to self-regulate, Church says. He adds he is not particularly a fan of germ-line editing, because he thinks there are other, less expensive ways to accomplish most of the same medical benefits—and because proving its safety and effectiveness would require decades of waiting for gene-edited children to grow up.

Jennifer Doudna, who discovered the gene-editing potential of CRISPR–Cas9 in 2012, did not sign onto the commentary, but her co-discoverer Emmanuelle Charpentier did. Doudna, a professor of biochemistry at the University of California, Berkeley, who called for a moratorium on germ-line editing back in 2015, says she did not sign because she thinks the time for such a step has passed—and that what is needed now is action. “We have to put in place international requirements and consequences to crossing the line with those requirements, ensuring that we don’t see premature use of human germ-line editing in the near future,” she says.

Doudna says that if scientists do proceed with germ-line editing at some point (and she thinks science is nowhere near the level of safe or ethical human germ-line editing now), there should be standards to ensure their edits are accurate, parents are properly informed of the risks and benefits, and gene-edited children will be monitored so scientists can learn from their experiences. She thinks there also needs to be clearly articulated consequences for any scientist who violates the rules—such as depriving them of research funding, closing their academic labs and denying them the ability to publish any findings in a scholarly journal. All those things have already happened to He Jiankui, but when he set out to gene edit the babies he had assumed the reaction would be far more positive.

“It’s not clear that he recognized before he did his work that he would face those types of consequences,” Doudna says. “That’s what needs to change.”