Many immigrant parents seek to bring their own parents here to help with childcare while they toil in grueling jobs, two sociologists recently wrote in The New York Times. President Trump wants to stop them.

Citing security concerns, President Trump is trying to make it harder for immigrants to bring their parents and other relatives here—a practice he derisively calls “chain migration.”

But his proposals “reflect a fundamental misunderstanding of 21st-century American families and contradict the principle of family unity that has guided American immigration policy for the last 50 years,” two sociologists recently argued in The New York Times.

Many immigrant parents seek to bring their own parents here to help care for their children while they work long shifts in grueling jobs, according to Stacey Torres and Xuemei Cao.

“The support of family caregivers may be invisible to outsiders, but it is essential for the well-being of transnational families, especially in a country that lacks a system of affordable child care. The Republican plans to restrict family-based migration won’t help Americans—they will hurt Americans, by depriving many of our youngest citizens of the social, psychological, and economic benefits of strong extended family ties.”

Already, Trump has banned nearly all citizens of Iran, Syria, Yemen, Libya, and Somalia from even visiting the United States, even if their grandchildren are American citizens. This “Muslim ban” was upheld by the Supreme Court in June.

As Torres and Cao note, Melania Trump, who is from Slovenia, recently helped her parents become American citizens, thus enabling them to be near her and the President’s son, Baron.