The labor migration network center upon the USA and Canada differs from those described above. Levels of living gradients to the south are very sleep, giving rise to a continuing problem of illegal movement ( Keely and Elwell, 1981 ) Furthermore the immigration tends to have a marked ethnic character leading to major integration problems ( e.g. Portes , 1981 ) Political relationships are especially important affecting flows between the USA and Canada are in little need of further supplies of unskilled labor, except in certain circumstances such as the scasonal immigration of agricultural labor in the south- west ( Ranney and Kossoudji, 1983 ), the emphasis is on the import of skilled workers but these are often those most needed by origin countries themselves. Morales ( 1983 ) has pointed out the transitional role of less- skilled undocumented aliens in increasing the flexibility of employers in highly developed industries such as car manufacturing, who seek to reduce employee numbers and substitute capital for labor.