SABANETA, Dominican Republic — For decades, the people of Barrio Cementerio, a neighborhood divided evenly between Dominicans and Haitians, have shared a peaceful coexistence. Proximity smothered prejudice: Working side by side and raising families together helped keep tensions in check.

That is changing now. A government plan that could deport tens, if not hundreds, of thousands of people of Haitian descent from the Dominican Republic has started to tear at the unity that once bound this place, forcing residents to pick a side.

A bitter landlord stopped renting to a Haitian tenant. The head of the local Red Cross says the deportations are long overdue, while a gang leader promises to hide his Haitian friends from the authorities. A Dominican husband fears losing his wife and their children, who have no papers. A police officer agonizes over the prospect of having to deport his best friend, who came to this country illegally from Haiti.

“I have no choice,” said John Tapia Thomas, the police officer, outside his friend’s makeshift Internet cafe. “It saddens me to think about being ordered to detain someone I really care about. It will be hard not to make exceptions, but I have to go about my job as professionally as I can.”