These "underclass" jobs, which have a disproportionate number of undocumented immigrants, include harvesting crops, unskilled labor in landscaping and construction, house-cleaning, and maid and busboy work in hotels and restaurants. Death by exposure occurs in the deserts of Southwestern United States during the hot summer season. Economic results of migration and Economic migrant Research on the economic effects of illegal immigrants is scant but existing studies suggests that the effects are positive for the native population,   and public coffers. Exploitation of labour Most countries have laws requiring workers to have proper documentation, often intended to prevent or minimize the employment of undocumented immigrants. Massey argues that this refutes claims that undocumented immigrants are "lowering wages" or stealing jobs from native-born workers, and that it instead shows that undocumented immigrants "take jobs that no one else wants. However, the advantage decreases with the skill level of the firm's workers,  Reasons for illegal immigration[ edit ] Trade liberalization[ edit ] In recent years, developing countries have pursued the benefits of globalization by adopting measures to liberalize trade. The poorest classes in a developing country may lack the resources needed to mount an attempt to cross illegally, or the connections to friends or family already in the destination country. Census Bureau, undocumented immigrants in the United States often work in dangerous industries such as agriculture and construction. Unauthorised arrival into another country may be prompted by the need to escape civil war or repression in the country of origin. There are also examples where natural disasters and overpopulation can amplify poverty -driven migration flows. In , the military junta stripped the Rohingya of their Myanmar citizenship, classing them as illegal immigrants and rendering them stateless. This may result in family members entering illegally in order to reunify. According to the Refugee Convention refugees should be exempted from immigration laws and should expect protection from the country they entered. Denaturalization In a news story, the CSM reported, "The estimated , Rohingya , one of the most miserable and oppressed minorities in the world, are deeply resentful of their almost complete absence of civil rights in Myanmar. Sex trafficking Some people forced into sexual slavery face challenges of charges of illegal immigration. Research indicates that the advantage to firms from employing undocumented immigrants increases as more firms in the industry do so, further increases with the breadth of a firm's market, and also with the labor intensity of the firm's production process. However, as even these "underclass" jobs have higher relative wages than those in home countries they are still attractive for undocumented immigrants and since many undocumented immigrants often anticipate working only temporarily in the destination country, the lack of opportunity for advancement is seen by many as less of a problem.