Some groups representing Muslims and Arab-Americans are concerned that some people may be targeted because of their ethnicity or religious beliefs.
"If somebody breaks the law in terms of their immigration status, they should pay the price," said Ibrahim Hooper, spokesman for the Council on American-Islamic Relations.
"We can only hope they are not targeting people based on whether they are Muslim."
Since its inception in June 2003, the division's Compliance Enforcement Unit has opened more than 5,200 investigations of visa violators nationwide.
Of those apprehended, 359 are considered "priority arrests" -- those with possible links to terrorism or criminal histories.
The stepped-up initiative is one of many government efforts intensified because of intelligence reports indicating Al Qaeda is determined to attack inside the United States before the Nov. 2 election.
The FBI has conducted more than 13,000 interviews this year, with more to come, in an effort to gather intelligence about the potential plot.
Special attention is being paid to the hunt for immigration violators because some hijackers involved in the terrorist attacks of Sept. 11, 2001, had violated terms of their visas.
One was Hani Hanjour, who did not show up for English classes as required by his December 2000 visa.
About nine months later, he piloted American Airlines Flight 77 into the Pentagon.
In its final report, the Sept. 11 commission said the government could have "potentially excluded, removed, or come into further contact with several hijackers" if a better immigration tracking system had existed.
Since the attacks, the government has created several systems for tracking foreigners with visas.
They can alert agents to possible violators, such as students who drop out of school and business people who do not do the work they promised when they arrived.
Advocates for Muslims and Arab-Americans say they do not fault the government for pursuing people who are in the United States illegally.
