In 1980, some 125,000 Cubans were allowed to leave the country to the United States from the port of Mariel. These immigrants, half of whom permanently settled in Miami, increased Miami's overall labor force by 7 percent in under half a year.
Typical econometric studies of the effect of immigration rely on cross-city differences in proportion of immigrants in the labor force. However causation is difficult to ascertain since immigrants may choose to settle in cities with more vibrant labor markets. The drastic and sudden increase in number of immigrants in Miami serves as a nice natural experiment to assess the labor market effects of increase immigration.
By comparing Miami with other cities (Atlanta, LA, Houston, and Tampa), David Card finds that the Mariel immigration had essentially no effect on the wages or employment outcomes of non-Cuban workers in the Miami labor market.
Card also finds a decline in Cuban wages in Miami, but this is entirely attributable to the fact that Mariel immigrants earn about 1/3 less than other existing Cuban immigrants.
What could account for the absence of adverse effects on the labor market? First, native workers may have moved out of Miami in response to the influx of immigrants. Second, capital may have moved into Miami to take advantage of the larger pool of labor.
The massive influx of Soviet Jews into Israel following the collapse of the Soviet Union also brought about very little adverse effects on the employment outcomes in the Israeli labor market.