But the Puerto Rican citizenship invented for Puerto Rico clashed with various federal citizenship and nationality laws. For example, the prevailing passport law of the period limited the issuance of passports to U.S. citizens, so Puerto Rican merchants who sought to travel found themselves unable to acquire a U.S. passport. In response to this and other administrative problems, Congress in 1906 began to enact legislation granting individual Puerto Ricans the ability to acquire U.S. citizenship by traveling to the mainland and undergoing the prevailing naturalization process. In effect, Puerto Ricans were able to acquire citizenship individually, just like any other racially eligible immigrant. This was the first law granting Puerto Ricans U.S. citizenship.