Zhang with a baby boy born to a Jordanian couple using 3-Parent IVF NEW HOPE FERTILITY CLINICThe US Food and Drug Administration condemned New York fertility doctor John Zhang for promoting a controversial procedure that combines DNA from an egg donor with DNA from a mother and father—dubbed the three-person or three-parent baby technique—CNN reports. In a letter last week (August 4), the FDA asks Zhang to detail how he plans to resolve the situation.

The procedure, which can help parents elude genetic disorders, was successfully used on a Jordanian couple who wanted a child without passing on the mother’s fatal neurological disorder. The couple gave birth to a baby boy a year ago.

See “Details of First Three-Parent IVF Revealed

Zhang’s company and fertility clinic keep marketing the procedure despite previously pledging to refrain from conducting it in the U.S., the Associated Press reports. His start-up company, Darwin Life, also touts the technique—described as spindle nuclear transfer—as a means to help older women get pregnant, reports MIT Technology Review.

The procedure entails removing the bulk of the donor egg’s genetic material and replacing it with the mother’s chromosomes. The donor’s mitochondrial DNA still remains. Once fertilized, the modified embryo contains three individuals’ genetic contributions.

“This is a biologically extreme and risky procedure,” executive director of the Center for Genetics and Society Marcy Darnovsky tells MIT Technology Review.

The controversy surrounding this technique stems from the lack of empirical data backing its safety and efficacy, coupled with the belief that it constitutes a form of genetic modification. It’s currently banned in the U.S., and Congress has barred regulators from considering it in this year’s omnibus spending bill, according to BuzzFeed, although it’s approved in the U.K. on a restricted basis.