BARCELONA, Spain — On sunny weekends, dozens of sidewalk vendors line up along the seafront promenade in Barcelona, offering wares like purportedly designer-name sunglasses, clothing and other knickknacks, usually counterfeit.

The vendors, known as manteros, epitomize a quandary facing the authorities: It is one thing to debate whether to allow more migrants into the European Union, but quite another to agree on what to do with them once they arrive.

Most manteros are migrants from Africa who have often risked their lives fleeing violence or poverty. But many find when they reach the European Union that landing a regular job without the correct papers is almost impossible — especially in high-unemployment countries like Spain.