When people move from one country to another country, the process is called immigration & they called immigrants. Immigration can be done for the purpose of work or stay or travel.
Every country has their own rules & quotas for immigration think the situation when all people from particular country start coming you r country, there will be so many problems. You might have sufficient food & place to stay when these people (immigrants) were not here. This is the reason why authority needs to put stop signal for immigration.
There are many immigration laws for US called federal laws of immigration. IRCA Immigration reform control act 1926, talks about all the rules and regulations.
1) IRCS act 1986 talks about hiring unauthorized worker, who might be Immigrated from other country.
2) IRCS act 1990: In this acts valid visas are increased upto 675000 people which allots diversified 55000 visas to immigrant from underserved countries.
3) Illegal immigration reform under IIRAIRA 1996 says 3-10 year ban on returning USA, if caught without documentation.
4) Legal immigration family & life equity act 2000: This was a dream act for all immigrants, by ths amendment they can bring their family member, they not allow to work but stay along with.
Illegal immigration is not problem of US but many of the countries. These Aliens are not citizen of any particular country (other than the country they born right?), these aliens not only create social, economic Burdon on our country but could be dangerous as well. These if any tom-dic-harry stay with you in your house wills you feel safe & comfortable? NO! Same way in our country we saw any immigrants we should check their passport for their identity & citizenship.