The Dominican Republic's top court has handed down a decision stripping citizenship from anyone born to migrants who came to the Dominican Republic illegally, an action that overwhelmingly affects Haitians.
The ruling by the Constitutional Court this week is final and cannot be appealed. The decision applies to anyone born after 1929.
Dominican officials said it would take no more than two years to decide who would be excluded from citizenship.
The ruling potentially affects tens of thousands of Haitian Dominicans, leaving them stateless and facing mass deportation to Haiti, a place where many of them have no ties or citizenship.
David Abraham, a law professor at the University of Miami, told the Associated Press "the fear of the Dominican Republic, of being pulled down to the level of Haiti economically and the 'blackening' of the country has been an obsession of Dominican politicians for well over a century."
Haiti is one of the world's poorest countries.
Meanwhile, the Dominican military announced it has deported 47,700 Haitians caught entering the country in the past year, more than double the nearly 21,000 deported in the previous year.
Spanish-speaking Dominicans and Creole-speaking Haitians share the Caribbean island of Hispaniola and have a long history of conflict and tense relations.
Some information for this report was provided by AP and AFP.