SAN FRANCISCO — U.S. Immigration and Customs Enforcement agents this week served notices of inspection at 77 Northern California businesses in an effort to root out illegal workers.

The so-called I-9 audit notices were delivered to businesses in San Francisco, San Jose and Sacramento, said ICE spokesman James Schwab. He would not name the businesses.

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Mariela Garcia, community organizer at Sacred Heart Community Services in San Jose, said Santa Clara County’s Rapid Response Network received calls this week about workplace audits. The network was able to confirm that two businesses were audited, but Garcia did not name them.

“It’s put people in a lot of panic,” Garcia said. “We have people who are quitting their jobs.”

A notice of inspection alerts a business owner that Homeland Security Investigations, a division of ICE, is going to audit their hiring records to determine if they are in compliance with the law, Schwab said. Employers are required to produce their company’s I-9s within three days, after which an inspection is conducted.

Under U.S. law, employers must have an I-9 form on hand for each employee, whether citizen or non-citizen, verifying their identity and authorization to work. Employees are supposed to produce valid identification such as a Social Security card to prove they are in the U.S. legally. In the audits, federal agents may ask to examine the employees’ proof of identity and work authorization.

The audits could lead to criminal charges or fines if businesses cannot produce valid forms, and are in keeping with ICE Deputy Director Tom Homan’s previous statement that he has directed HSI to step up worksite enforcement.

“The actions taken this week reflect HSI’s stepped-up efforts to enforce the laws that prohibit businesses from hiring illegal workers,” Schwab said.

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“HSI’s worksite enforcement strategy is focused on protecting jobs for U.S. citizens and others who are lawfully employed,” he continued, “eliminating unfair competitive advantages for companies that hire an illegal workforce, and strengthening public safety and national security.”

Last month, agents served notices of inspection at 7-Eleven stores across the country, including locations in Santa Clara, Santa Rosa, Napa, Sebastopol, Suisun City and Petaluma.

In fiscal year 2017, HSI conducted 1,360 I-9 audits and made 139 criminal arrests and 172 administrative arrests. Businesses were ordered to pay $97.6 million in judicial forfeiture, fines and restitution and $7.8 million in civil fines, according to an ICE press release.

No arrests have yet been made in connection with this week’s audits, Schwab said.

A renewed national debate over immigration has seen questions resurface about the effectiveness of E-Verify, a 21-year-old electronic program designed to filter out undocumented immigrants who apply for jobs. Some immigration experts have likened it to a political fig leaf, with so many significant flaws and loopholes that it allows employers to continue to knowingly hire undocumented workers with few repercussions.

However, a “large portion” of employers don’t use E-Verify for new hires because they know government audits of traditional paper forms are so few and far between, said Alex Nowrasteh, an immigration policy analyst at Cato Institute’s Center for Global Liberty and Prosperity, in an interview with this news organization earlier last month.

Daniel Costa, director of immigration law and policy research for the Economic Policy Institute, a pro-labor think tank based in Washington, D.C., agreed with that assessment. He noted earlier this month that even though audits of the I-9 forms soared during the Obama administration, an average of only 2,000 workplaces, including some enrolled in E-Verify, were audited annually during the eight years Barack Obama was president.

According to U.S. Citizenship and Immigration Services, which oversees the E-Verify program, an estimated 763,500 employers were taking part in the program as of Jan. 16.

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When asked what the Rapid Response Network is telling immigrants who are terrified to go to work, Garcia said, “it would be easier to advise them if the threat weren’t so real.”