Immigration consists mainly of Spanish, Portuguese, and French nationals who intend to work in Andorra; these groups make up some 70% of the population. Spanish nationals account for the largest group of foreign residents, comprising approximately 43% of the population in 1999. There is also a small but rapidly growing group of African immigrants, especially from North Africa, working mostly in agriculture and construction. Immigrant workers are supposed to hold temporary work authorization permits, which are valid only as long as the job exists for which the permit was obtained. However, more than 4,000 immigrants did not have work permits in 1999, due to the fact that the quota for immigration is not as high as the number of workers needed in the country. In 1999, the net migration rate was 17.61 migrants per 1,000 population. In 2000, approximately 81% of the population was not born in Andorra. The government views the migration levels as satisfactory.