A judge today halted federally funded research of human embryonic stem cells, which had been approved under guidelines issued by President Obama shortly after his inauguration.
The temporary injunction, approved by U.S. District Court Judge Royce Lamberth, takes effect as a group of doctors, who work exclusively with adult stem cells, and Christian medical groups, ask a court to rule that the government's funding for research involving embryonic stem cells is against the law.
The Justice Department said it is "reviewing the judge's ruling."
At the heart of the legal battle is a law known as the Dickey-Wicker Amendment, which prohibits federally funded research in which a human embryo is "destroyed, discarded, or knowingly subject to risk of injury or death greater than that allowed under applicable regulations."
The measure has been attached to every appropriations bill for the Department of Health and Human Services since 1996. The department oversees the federal government's primary health research arm, the National Institutes of Health.
The plaintiffs have argued working with embryonic stem cells by nature depends upon the destruction of an embryo, and that the new guidelines therefore violate the law.
"If one step or 'piece of research' of an [embryonic stem cell] research project results in the destruction of an embryo, the entire project is precluded from receiving federal funding by the Dickey-Wicker Amendment," Lamberth wrote.
"Because ESC research requires the derivation of ESCs, ESC research is research in which an embryo is destroyed," the judge wrote. "Accordingly, the Court concludes that, by allowing federal funding of ESC research, the Guidelines are in violation of the Dickey-Wicker Amendment."
Stem cell research is widely believed to have the potential to significantly advance treatment of human diseases and disabilities. There are three different types of stem cells, but only one type -- embryonic -- requires the controversial destruction of a human embryo.
President George W. Bush banned federal funding of embryonic stem cell research in 2001, citing "moral concerns raised by the new frontier of human embryonic stem cell research. Even the most noble ends don't justify the means."
But President Obama reversed the policy by executive order in March 2009, saying federal agencies "may support and conduct responsible, scientifically worthy human stem cell research, including human embryonic stem research, to the extent permitted by law.
"In recent years, when it comes to stem cell research, rather than furthering discovery, our government has forced what I believe is a false choice between sound science and moral values," he said. "In this case, I believe the two are not inconsistent."
The National Institutes of Health have since allowed for "funding for research using human embryonic stem cells that were derived from human embryos created by in vitro fertilization (IVF) for reproductive purposes and were no longer needed for that purpose."
Nearly six in 10 Americans support loosening restrictions on federal funding of stem cell research. Proponents of stem cell research say Obama's order is a promising sign that progress can be made after a more-than-eight-year stalemate, while others say it is only a tiny step. Anti-abortion groups say the research is unethical and unreliable.
Lamberth had originally dismissed the case, saying the plaintiffs lacked standing to sue the government. An appeals court reversed that decision, agreeing to hear the case and forcing Lamberth to reconsider a request to issue a temporary injunction.
ABC News' Jason Ryan contributed to this report.