President Obama's administration announced Thursday that it plans to focus on deporting illegal immigrants with dangerous histories, as opposed to those who do not have criminal records and pose no threat to American society.

The ruling applies to illegal immigrants who are currently in the process of facing deportation. The Obama administration will judge on a case-by-case basis whether an illegal immigrant facing deportation may stay in the United States and possibly qualify for a work permit or be deported.

Approximately 300,000 cases will be reviewed.

Janet Napolitano, secretary of the Department of Homeland Security, wrote to a group of lawmakers. The Associated Press obtained a copy of the letter.

From a law enforcement and public safety perspective, DHS enforcement resources must continue to be focused on our highest priorities, Napolitano wrote. Doing otherwise hinders our public safety mission -- clogging immigration court dockets and diverting DHS enforcement resources away from the individuals who pose a threat to public safety.

Harsh criticism of the ruling has surfaced from proponents of tighter border control who want to rid the country of illegal immigrants. They see the move as a disregard for state law and one that sidesteps Congress.

This plan amounts to backdoor amnesty for hundreds of thousands - if not millions - of illegal aliens, Arizona governor Jan Brewer said in a statement.

Americans for Legal Immigration denounced the move as a high crime on their Web site.

Obama just nullified the elections, your votes, the U.S. Constitution, Congress, and every letter, fax, or call you have directed at Congress to defeat this AMNESTY legislation 8 times in the last five years, the group wrote.

The Federation for American Immigration Reform referred to the review as a blatant usurpation of Congress' authority.  

Today's policy announcement clearly demonstrates the Obama administration's defiance of both the constitutional separation of powers and the will of the American public in its relentless effort to gain amnesty for illegal aliens, FAIR president Dan Stein said in a statement.

Cecilia Muñoz, White House Director of Intergovernmental Affairs, wrote on the White House blog about the ruling and answered questions via Twitter.

If you were running a law enforcement agency anywhere in the world, you would target those who pose the greatest harm before those who do not, she blogged. Our immigration enforcement work is focused the same way.