The United States Constitution does not define federal power over immigration. However, courts have deemed it a "plenary power" of a sovereign nation. A plenary power is an absolute power that has been granted without limitations to a a body or a person. As a result, United States immigration law has developed extensively, often free of judicial review.

The Constitution creates a government of specific powers, and states that Congress has the power "(t)o establish a uniform Rule of Naturalization … throughout the United States." Thus, the Constitution gives Congress the power to determine which foreigners can become citizens, and under what conditions they may gain citizenship. The Constitution, however, is silent on immigration. This means that, although the federal government has the direct power to grant citizenship, it is not explicitly granted a general power to exclude or remove noncitizens from the United States.

Nevertheless, the courts have allowed the federal government to exercise such a power. At various points in time this power over immigration has been said to derive from various clauses in the Constitution.

As early as 1798, Congress acted on immigration. These actions took place with the United States on the brink of war with France. New laws allowed the president to imprison or deport people who immigrated illegally, and who were deemed dangerous to "peace and safety" (Alien Friends Act of 1798). It could also apply to citizens of a nation with which the United States was at war (Enemy Alien Act of 1798). It also increased the residency requirement for naturalization from five to 14 years (Naturalization Act of 1798).

Still, for most of the nation's first century, the source of Congress' power to act on immigration was irrelevant, since immigrants were allowed in without restriction. However, in 1875, Congress barred the immigration of convicts and prostitutes. In 1882, Congress forbade immigration of people who were very poor, as well as people with mental illnesses or disabilities.

Federal Power Based on "Incident Of Sovereignty"

Also in 1882, Congress passed the Chinese Exclusion Act, prohibiting immigration of Chinese people. As this law was challenged in court, the Supreme Court began to articulate a basis for federal power to control immigration. In that and subsequent cases, the Supreme Court has held that the power to exclude people who have immigrated illegally is not explicitly set forth in the Constitution. Instead, it is a power rendered by an "incident of sovereignty."

In Chae Chan Ping v. United States, 130 U.S. 581 (1889), the Supreme Court stated:

"That the government of the United States, through the action of the legislative department, can exclude aliens from its territory is a proposition which we do not think open to controversy. Jurisdiction over its own territory to that extent is an incident of every independent nation. It is a part of its independence.

"If it could not exclude aliens, it would be to that extent subject to the control of another power …"

In Fong Yue Ting v. United States, 149 U.S. 698 (1893), the Supreme Court further held:

"The right of a nation to expel or deport foreigners who have not been naturalized, or taken any steps towards becoming citizens of the country, rests upon the same grounds, and is as absolute and unqualified as the right to prohibit and prevent their entrance into the country."

States Cannot Regulate Immigration

The Supreme Court has ruled deportation is an exclusively federal power. In other words, individual states may not regulate immigration:

"The Federal Government has broad constitutional powers in determining what aliens shall be admitted to the United States, the period they may remain, regulation of their conduct before naturalization, and the terms and conditions of their naturalization … Under the Constitution, the states are granted no such powers ..."

The nature of the congressional power over immigration, the Supreme Court has held, is "plenary." This means that the decisions of Congress concerning immigration are relatively free of review by the courts. Still, the Court has indicated that the plenary power is subject to constitutional limits.

Since the 1880s, Congress has exercised its plenary power extensively. In the 1920s, immigration was based on a national origin quota system. The number of immigrants allowed was limited based on how many immigrants from a nation are already in the U.S., based on past U.S. census figures. As a consequence, immigration was relatively higher from Northern and Western Europe than other areas.

Today, the federal power over immigration is set forth in the Immigration and Naturalization Act. As originally enacted in 1952, this law maintained certain exclusions and also altered the previous national origins quota. In this instance, a quota refers to a fixed minimum or maximum amount of immigrants who can enter the country each year.

Family Members Get Priority

Amendments in 1965 eliminated national origin quotas, instead emphasizing family reunification. As a result, the immigration system prioritized immigration of family members of those already here. Subsequent amendments in 1986, 1990, and 1996 granted partial amnesty to immigrants who came into the country illegally, which in turn increased levels of immigration. The Patriot Act of 2001 toughened background checks for admittance to the United States.

In addition, the United States has been the global leader in resettling refugees. A refugee is defined as an individual outside his or her country of citizenship who is unwilling to return because of a well-founded fear of persecution. Those people may feel threatened in their home country based on race, religion, nationality, membership in a particular social group, or political opinion. Historically, the United States has taken in more refugees each year than the rest of the world combined.

U.S. policy on immigration has swung back and forth between open admissions and greater restrictions. Some of this confusion is due to the unclear constitutional basis for federal authority in this area. The Constitution does not directly say which branch of government is in charge. Therefore each branch has, at various times, attempted to assert its authority.