BRUSSELS—A group of European pro-life organizations is mobilizing against embryonic stem cell research in a way that the European Commission cannot ignore. One of Us, a so-called European citizens’ initiative, has collected 1.7 million signatures from all 28 E.U. member states for a proposal that would block funding for research in which embryos are destroyed; under E.U. rules, the European Commission must now consider turning the proposal into legislation.

Research commissioner Máire Geoghegan-Quinn will meet the organizers of the initiative here today; on Thursday, they will defend their case during a public hearing at the European Parliament. The commission has until 28 May to spell out its response.

The proposal is a direct attack on a delicate compromise over the use of embryonic cells in research, a topic on which the union is sharply divided. “Any roll back of this agreement would be a major step backwards for research across regenerative medicine, reproductive health and genetic disease, and delay the development of much needed treatments for a host of untreatable conditions,” said a group of 31 research organizations and universities from across Europe today in a statement. The group, led by the Wellcome Trust, urged the commission and the Parliament to oppose the initiative.

European citizens’ initiatives, a democratic novelty introduced in 2012, allow citizens to propose E.U. legislation; if a proposal gets at least 1 million verified signatures from seven or more member states, the commission has to consider turning it into law. (One of Us is only the second one to reach that threshold; the first one called on the commission to implement the human right to water and sanitation.)

E.U. member states have different regulations in the area of embryonic stem cell research, ranging from very permissive—for example in Belgium, Sweden, and the United Kingdom, where creating embryos for research purposes is allowed—to very restrictive—as in Poland and Lithuania, where research with embryonic stem cells is illegal.

As far as E.U. funding is concerned, member states have agreed to disagree. Under the European Union’s 7-year research program Horizon 2020, which started this year, the union does not sponsor research that is illegal in the country where it would take place. In addition, the commission never funds research activities that create human embryos for research purposes. But the proponents of the One of Us initiative say this arrangement is too lax; they argue that no E.U. money at all should go to research activities that destroy human embryos. This would block funding for stem cell research using leftover embryos from in vitro fertilization.

“The dogma underlying [the plea] is that as soon as the ovum is [fertilized], there is a person with a soul,” says Charles Susanne, a retired biology and anthropology professor at the Université Libre de Bruxelles who now studies bioethical issues. “Based on this principle, it’s natural to reject abortion or research using embryos of no more than 4 or 8 cells.”

In its legislative proposal, One of Us refers to the 2011 ruling of the European Court of Justice in a case known as Brüstle v. Greenpeace, which stated that processes and products involving human embryonic stem cells are not patentable in the European Union. The judgment “indicates that fecundation is the beginning of human life and in the name of human dignity excludes the patenting of any procedure that involves or supposes the destruction of a human embryo,” the organizers write. The European Union should apply that principle across the board, they argue.

Julian Hitchcock, a life sciences lawyer at the London-based firm Lawford Davies Denoon, says that argument can’t withstand legal scrutiny. The court’s ruling was limited to biotechnology patents and can’t be read as a general statement about where life and human dignity begin, Hitchcock says.

Under the previous E.U. research program, from 2007 to 2013, the European Union spent €156.7 million on 27 collaborative projects in health research involving the use of human embryonic stem cells, a commission spokesman says. “Europe is currently a global leader in these competitive research areas, and clinical trials are already underway resulting from stem cell research,” today’s joint statement from the scientific organizations says. “Any move to restrict research using embryos will threaten this position, and prevent researchers developing vital treatments for patients.”

Observers say it is hard to predict if the Eropean Commission will reopen discussions on its hard-won agreement. “A priori I would hope not, since the decision has already been made … to keep the compromise” under Horizon 2020, Susanne says.

One of Us, which boasted the support of Pope Benedict XVI, says it has received about €160,000 from three pro-life foundations in Spain and Italy in the past 2 years.