Special agents with Immigration and Customs Enforcement's Homeland Security Investigations team conducted surprise inspections at nearly 100 7-Eleven convenient stores Wednesday as part of a national effort to ensure those businesses are hiring employees who are legally authorized to work in the country.

As a result, 21 people were administratively arrested on suspicion of being in the U.S. illegally, and were given court dates.

"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," ICE Deputy Director Thomas D. Homan said in a statement.

ICE showed up without warning to audit the 7-Elevens' I-9 documents. As part of the surprise audits, agents spoke with managers and employees at every location.

"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," Homan added.

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

The HSI investigation and service of notices of inspection was meant as a follow-up to a company-wide problem that was discovered in 2013.

Five years ago, the agency arrested nine franchise owners and managers for conspiring to commit wire fraud, stealing identities, and concealing and harboring illegal immigrants employed at 7-Eleven stores.

"Today’s service of NOIs throughout the United States serves as a follow-up to ensure the company has taken the proper steps towards more responsible hiring and employment practices," the agency added.