Investigators say telemarketing tactics were used to collect random money from immigrants claiming their relatives had been kidnapped.
In reality, no one had been snatched and the callers didn't even know who they were dialing.
According to federal documents, callers in Tijuana, Mexico used about 30 different San Diego phone numbers to make the calls, up to 5,000 a day.
"They would just randomly run through a sequence of number, like 1 to 100," said Daniel Page, assistant special agent in charge of U.S. Immigration and Customs and Enforcement's Homeland Security Investigations unit in San Diego."
The callers demanded that money be wired, saying they were holding a relative who had been heading to the U.S. illegally.
"They're just like your professional telemarketer. They have a script. 'You need to pay this money. If you don't, something's going to happen," said Page.
While the success rate was small, those who took the bait usually paid between $1,000 and $3,000.
Authorities said the suspects targeted the Washington, D.C. area, because it is home to large numbers of Central American immigrants whose migrant relatives are often out of contact during the long journey north.
The four charged are Ruth Graciela Reygoza, 63, of Chula Vista; Maria del Carmen Pulido, 24, of East Los Angeles; and brothers Adrian Rocha, 25, and Juan Rocha, 23, Americans who live in Tijuana. They are accused of picking up random payments in the San Diego area and bringing the money to Tijuana.
A detention hearing for the four suspects is scheduled for Thursday.
The Associated Press contributed to this report.