Immigration has lowered wages in the United States as low-skilled newcomers have depressed the earnings of low-paid Americans, increasing the gap relative to the highest-paid.

According to Statistics Canada, the differences in skill mixes between Canada and the United States have been caused by differences in immigration policies during the last four decades.

Canadian immigration policies since the 1960s have encouraged high-skilled workers to come to the country. During the same period, American immigration policy has emphasised family reunification, resulting in a disproportionate number of low-skilled immigrants.

Significant illegal immigration to the United States – an estimated 10.3 million between 1965 and 2005 – mostly from Mexico, has also contributed to the tendency for US immigrant workers to be lower-skilled than those who have entered Canada.

Immigration to the United States has also tended to increase the supply of younger workers; the opposite has been seen in Canada.

Between 1980 and 2000, immigration increased the male labor force by 13.2% in Canada and 11.1% in the United States. In each country, a migration-induced increase of 10% in the labour supply was associated with a 3% to 4% drop in weekly earnings.