U.S. Immigration and Customs Enforcement agents blitzed dozens of 7-Eleven stores before dawn Wednesday to interview employees and deliver audit notifications, carrying out what the agency said was the largest operation targeting an employer since President Donald Trump took office.

ICE said its agents showed up at 98 stores and made 21 arrests, describing the operation as a warning to other companies that may have unauthorized workers on their payroll.

“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 Homan, the agency’s top official, in a statement.

Homan characterized the operation as a new front in the Trump administration’s broader immigration crackdown and its effort to increase deportations. ICE agents have made 40 percent more arrests in the past year.

“Businesses that hire illegal workers are a pull factor for illegal immigration and we are working hard to remove this magnet,” Homan’s statement said. “ICE will continue its efforts to protect jobs for American workers by eliminating unfair competitive advantages for companies that exploit illegal immigration.”

ICE said it sent agents Wednesday to deliver audit notifications and conduct interviews at 6 a.m., temporarily shutting down 7-Eleven stores in Washington, D.C., and 17 states: California, Colorado, Delaware, Florida, Illinois, Indiana, Maryland, Michigan, Missouri, Nevada, New Jersey, New York, North Carolina, Oregon, Pennsylvania, Texas and Washington.

Irving, Texas-based 7-Eleven has more than 60,000 stores worldwide, including more than 8,600 in the U.S., according to its website. In a statement, the company said it was not responsible for the hiring decisions of individual franchise owners.

“7-Eleven Franchisees are independent business owners and are solely responsible for their employees including deciding who to hire and verifying their eligibility to work in the United States,” the company said in an emailed statement.

“As part of the 7-Eleven franchise agreement, 7-Eleven requires all franchise business owners to comply with all federal, state and local employment laws,” the statement said. “7-Eleven takes compliance with immigration laws seriously and has terminated the franchise agreements of franchisees convicted of violating these laws.”

Illegal hiring is rarely prosecuted, partly because investigations are time-consuming and convictions are difficult to achieve because employers can claim they were duped by fraudulent documents or intermediaries. Administrative fines are discounted by some as a business cost.

President George W. Bush’s administration aggressively pursued criminal investigations against employers in its final years with dramatic pre-dawn shows of force and large numbers of worker arrests. In 2008, agents arrived by helicopter at the Agriprocessors meatpacking plant in Postville, Iowa, and detained nearly 400 workers. Last month, Trump commuted the 27-year prison sentence of Sholom Rubashkin, former chief executive of what was the nation’s largest kosher meatpacking operation.

President Barack Obama’s administration more than doubled employer audits to more than 3,100 a year in 2013, shunning Bush’s flashier approach. John Sandweg, an acting ICE director under Obama, said significant fines instilled fear in employers and drained resources from other priorities.

Wednesday’s operation arose from 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.

Associated Press contributed.