STATEN ISLAND, N.Y. -- Immigration officials surprised several 7-Eleven locations on Staten Island before dawn Wednesday as part of a nationwide sweep to crack down on companies who hire undocumented workers.

The Advance has confirmed the agents visited at least two Port Richmond stores and another in Meiers Corners.

The action was part of a joint effort between the U.S. Immigration and Customs Enforcement (ICE) and Homeland Security at 98 locations across the country, including 16 in New York City, according to an ICE spokeswoman.

Special agents served audit notices and conducted interviews with workers and managers to make sure businesses are operating with employees who have proper work authorization.

Nationwide, 21 individuals suspected of being in the U.S. illegally were administratively arrested and given notices to appear in immigration court.

Numbers for Staten Island weren't immediately available, but workers at Staten Island 7-Eleven locations visited by the Advance said there were no arrests at their stores.

At the 1440 Forest Ave. spot, the owner said officials showed up at around 5 a.m. to check her employees' paperwork.

"We were good," she said, declining to give her name. "Everything checked out."

Agents visited the store at the corner of Victory Boulevard and Bradley Avenue at around 6 a.m. to check employment documents.

"They were here for like 15 minutes or so, then they left when everything was good," said the location's manager.

A manager at the 1252 Forest Ave. location would only confirm the agents were at the store early Wednesday morning.

Employees were unsure if officials were there to check immigration status or to verify employment.

A 7-Eleven worker at the corner store on Forest Avenue and Richmond Avenue in Graniteville said a customer told her his son was among those who were vetted in the probe at another site. Officials did not visit that location, though.

"He said they told him (the son) that he should carry his green card around with him," she said.

The franchise sites in Bulls Head, at the corner of Victory Boulevard and Richmond Avenue, and Sunnyside, near Clove Lakes Park, were not part of the early-morning sweep, workers said.

"I know they were checking green cards," said the manager at the Bulls Head location.

The audits took place in Washington, D.C, California, Colorado, Delaware, Florida, Illinois, Indiana, Maryland, Michigan, Missouri, Nevada, New Jersey, New York, North Carolina, Oregon, Pennsylvania, Texas, and Washington.

"Today's actions send a strong message to U.S. businesses that hire and employ an illegal workforce: ICE will enforce the law, and if you are found to be breaking the law, you will be held accountable," said Thomas D. Homan, ICE deputy director and senior official performing the duties of the director.

He continued: "Businesses that hire illegal workers are a pull factor for illegal immigration and we are working hard to remove this magnet. ICE will continue its efforts to protect jobs for American workers by eliminating unfair competitive advantages for companies that exploit illegal immigration."

Agents targeted the stores nationwide, broadening an investigation that began with a 4-year-old case against a franchisee on New York's Long Island.

Derek Benner, a top ICE official, told the Associated Press that Wednesday's operation was "the first of many" and "a harbinger of what's to come" for employers. He said there would be more employment audits and investigations, though there is no numerical goal.

"This is what we're gearing up for this year and what you're going to see more and more of is these large-scale compliance inspections, just for starters. From there, we will look at whether these cases warrant an administrative posture or criminal investigation," said Benner, acting head of ICE's Homeland Security Investigations, which oversees cases against employers.

The raids were due to a 2013 investigation that resulted in charges against nine 7-Eleven franchisees and managers in New York and Virginia. Eight have pleaded guilty and were ordered to pay more than $2.6 million in back wages, and the ninth was arrested in November.

In the 2013 investigations, managers used more than 25 stolen identities to employ at least 115 people in the country illegally, knowing they could pay below minimum wage, according to court documents. The documents say 7-Eleven corporate office does automated payroll, requiring franchisees provide employee names and Social Security numbers to pay workers through direct deposit or check.

The 7-Eleven stores served on Wednesday will be required to produce documents showing they required work authorization, which Benner said will become more common. Audits may lead to criminal charges or administrative penalties.

--Associated Press materials were used in this report.