The so-called "collateral arrests" involved people picked up by immigration agents while seeking fugitives such as drug smugglers, thieves, drunken drivers and others who flouted deportation orders.
When tracking down fugitives, authorities visit a suspect's last known address and often find other immigrants, who are then asked to prove they are legally entitled to live in the United States.
Supporters of such tactics say the government is just doing its job after years of neglect.
"God bless ‘em,'" said Peter Nunez, a former U.S. attorney in San Diego who teaches immigration policy at the University of San Diego. "They apparently decided to start with these fugitives. If you're going to find one (illegal immigrant), you're going to find 100."
Critics say the campaign against fugitive illegal immigrants ensnares many hard-working people who are in the country illegally but do not pose a danger.
"They're trying to sell it as something where they target (criminals) but it's become part of a larger dragnet," said Pedro Rios, director of the American Friends Service Committee's office in San Diego.
Dubbed "Operation Return to Sender," the crackdown began last May in cities across the nation. As of Feb. 23, it has resulted in 18,149 arrests of suspected illegal immigrants, most of whom were captured at home and in Hispanic neighborhoods.
But, according to figures from Immigration and Custom Enforcement, 37 percent of those cases, or 6,696 arrests, were "collateral" captives - people who just happened to be present when agents arrived. Such arrests account for more than half the total in four cities: Dallas and El Paso, Texas (59 percent); New York (54 percent); and San Diego (57 percent).
On Tuesday, ICE completed a two-week sting that targeted 300 fugitives in San Diego. Agents found 62 fugitives but took 297 other people into custody, bringing the total arrests to 359. The illegal immigrants were returned to their home countries or jailed while awaiting a court hearing.
The government defends the collateral arrests.
"We can't look the other way," said Robin Baker, ICE's director of detention and removals in San Diego. "We did that for too long."
The agency's guidelines are to make arrests in houses, not in the streets, Baker said, adding that agents do not randomly search communities for illegal immigrants.
For some, the stings evoke memories of immigration raids that fell out of favor in the 1980s. Since then, immigration authorities have stayed close to U.S. borders but are increasingly venturing into homes and workplaces across the country.
"It didn't happen for a good 15 years," Baker said. "Now that it's opening up again, people don't like it. They got used to us not being there."