The National Institutes of Health issued instructions on Friday for how scientists seeking grants for research using fetal tissue must comply with recent Trump administration restrictions on federal funding of such studies. The new requirements triggered an immediate outcry from leaders in the field.

In a notice spelling out the rule changes, NIH says that all grant applications and renewals for research relying on tissue collected from elective abortions must provide a detailed justification, documenting why no alternative methods could accomplish the same research goals. This and other changes for scientists at universities and other institutions take effect in two months.

The instructions also impose stringent requirements for how grant applicants must prove that women had given permission for their aborted fetuses to be donated for research.

And for the first time, the rules forbid graduate and postdoctoral students who receive NIH training funds from proposing fetal tissue research.

The instructions represent the first explanation of how the nation’s largest sponsor of biomedical research is setting in motion a decision announced in early June — made by President Trump over the objection of his top health and science advisers — to limit funding of research using fetal tissue. The decision appealed to social conservatives who are a critical part of the president’s base, and according to his aides, Trump regarded the restrictions as a way to augment his popularity with them for his reelection campaign.

The administration’s restrictions already forbid any new fetal tissue studies by scientists who work directly for NIH. For outside researchers, the administration is not outright ending such research but has created a new layer of ethics review for grant applications that qualify for funding based on the institutes’ usual scientific reviews. Friday’s notice provides details, though not complete information, about how the additional review will work.

Scientists say that fetal tissue research — often conducted in mice implanted with tissue from aborted fetuses — has proved crucial to help understand and develop therapies for diseases including HIV, cancers, Zika and Parkinson’s disease.

NIH spokeswoman Renate Myles said that the instructions were developed jointly by NIH and the Department of Health and Human Services and that the date when the rule changes go into effect — Sept. 25 — matches the institutes’ next grant cycle. Myles said the notice was sent to more than 100,000 researchers who have applied for various NIH funds.

She said the ethics advisory boards, which will carry out the new layer of review, are in the process of being formed. The notice reiterated administration officials’ announcement in June that they will be composed of “scientists, bio-ethicists and others” but did not elaborate.

Leading researchers who have opposed the restrictions immediately objected to the NIH instructions.

“Feasible but draconian,” said Larry Goldstein, a distinguished professor in the University of California at San Diego department of cellular and molecular medicine who has advised scientific groups that use fetal tissue. He pointed out that his grain of optimism that some grants will still be awarded was based on the hope that new ethics advisory panels will not be stacked with members opposing such research.

Other researchers had a darker view. “This could effectively shut down all research that uses fetal tissue,” said Mike McCune, an early fetal tissue researcher at the University of California at San Francisco who now is a senior adviser at the Gates Foundation.

McCune said the requirement that grant applicants document the lack of effective alternative research methods is “circular,” saying that fetal tissue would still be needed to do such comparisons. He pointed out that at a private meeting of fetal tissue researchers convened by NIH in December, federal officials concluded by agreeing to fund such comparative studies — which McCune predicted might be impossible under NIH’s new instructions.

Goldstein noted that the instructions require applicants to include the detailed justification for using fetal tissue as part of one section of a written “research strategy,” which has a 12-page limit. If NIH was interested in understanding the justification in detail, without weakening researchers’ overall applications, he said, “don’t put it in a page-limited part of the application, for crying out loud.”

He also said that the prohibition on fetal tissue studies by early-career scientists receiving NIH training funds “just seems terrible to me. You are going to have a generation of some of our best young scientists who have not had appropriate training in fetal tissue: When is it appropriate? When is it not?”

Deepak Srivastava, president of the International Society for Stem Cell Research, said the organization was still studying Friday’s guidance. “But it appears very problematic,” he said. “It will make it very difficult for researchers to seek NIH funding for research using fetal tissue.” Srivastava said the rules do not permit researchers who already have NIH grants to modify them “to use fetal tissue to answer important scientific questions that arise during their research.”

Friday’s notice does not give any indication that the instructions are preliminary. Still, several researchers said they intend to advocate for changes.

Otherwise, said Irving Weissman, a pioneer in stem cell research at Stanford University, “you write op-eds, you might move to another country, you obtain funding that is not NIH funding.”