Federal authorities have charged nine 7-Eleven owners and managers with exploiting illegal immigrants.
Investigators raided 14 stores on Long Island and in Virginia on Tuesday.
The workers were allegedly trafficked in from Pakistan to work at the stores, given stolen identities and forced to work long hours for less pay.
But officials say this is just the beginning.
Their investigation expands to more stores in other states.
"Agents are descending upon more than 40 7-Eleven franchises in seven states to collect data on their employees," said James Hayes Jr., a Department of Homeland Security official.
In a statement, 7-Eleven says it is cooperating with the investigation and will take "aggressive actions" against its employees.
The statement also says 7-Eleven is taking steps to assume corporate control of the stores involved.