Until the change, the United States had been allowing Haitians without visas to enter under a temporary humanitarian parole, a special concession owing to the social, economic and political troubles facing Haiti after the devastating 2010 earthquake. But on Sept. 22, amid a surge in Haitians from Brazil, the Obama administration said it was resuming the deportation of Haitians who presented themselves at border crossings without immigration documentation.

The policy change effectively shut the door on newly arriving undocumented Haitians, including men whose partners and children had already been admitted.

Immigrant advocates in San Diego said they had identified more than 50 families in that city alone who had been separated by the policy change, and they have appealed to Homeland Security officials to help reunite the families in the United States.

“The bottom line is that this was not a well-conceived policy,” said Andrea Guerrero, executive director of Alliance San Diego, a group that has been helping Haitians who have arrived from Brazil in recent months. “It seemed to have come down from one day to the next without a clear understanding of what was going on and what kind of impact it would have.”

The Department of Homeland Security did not immediately reply to written questions about the effect of the policy change.