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The Trump administration just blocked certain government scientists from using human fetal tissue in their research into diseases like HIV, Zika, and Parkinson’s disease.

The White House determined Wednesday that the National Institutes of Health scientists could find an alternative for their research, in a move that overrides scientists’ advice and gives a win to anti-abortion activists, who have long protested the use of fetal tissue in research.

“Promoting the dignity of human life from conception to natural death is one of the very top priorities of President Trump’s administration,” the Department of Health and Human Services, which announced the new fetal tissue rule, said in a news release Wednesday. (Trump has expressed support for restrictions on abortion, although he believes in exceptions in cases of rape or incest.)

Controversially to some, fetal tissue comes from elective abortions and would otherwise be discarded. Often used to produce mice that can model the human immune system, it’s been part of disease research and vaccine development for decades.

During a House hearing on fetal tissue in December, neuroscientist Sally Temple testified that there’s no adequate alternative for fetal tissue for many researchers, considering the tissue “is a different developmental stage, it has unique properties,” according to the Associated Press. The Trump administration said it will continue to research alternative tissues, and the NIH last year budgeted $20 million to looking for a suitable substitute.

An unnamed official told Fox News the administration believes there are other ways of acquiring fetal tissue, like using tissue from an umbilical cord or thymus. Ongoing government-funded research not conducted within NIH — at universities, for example — will not be impacted by the new rule, HHS said. Future applications for grant funding will have to go before a new ethics advisory board. For reasons that aren’t entirely clear, the administration also ended a years-long HIV research contract with the University of California at San Francisco on Wednesday.

The new rule will not impact privately funded research that utilizes fetal tissue from elective abortions.