"How do you know they're here illegally?" customer John Barnicoat, who is white, asked.
Others grew so angry that they left the store in tears and vowed never to return. One customer was so shocked by the clerk's behavior that he became determined to set him straight.
"If you can't deal with this country and how we accept other people, you don't belong working here," he told the clerk.
For some, the cashier's comments struck a personal chord.
Joanne Murphy, like many Americans, comes from a family of immigrants. So when Murphy, who is Irish-American, heard the cashier refuse the Hispanic women service by saying they weren't Americans, her response was passionate.
"Neither are my parents," Murphy said, shouting.
Merlange Rene, who is Dominican and Haitian, said she has experienced similar prejudice, even being told to go back to her own country.
"I have family that can't speak English," she told the cashier. "They're not here illegally."
For others, the scene in the deli violated the idea of treating every human being with respect.
"Give them what they want," Walter Orenczak said, after hearing the cashier accuse the day laborers of taking American jobs away. He is white.
"They are human beings and they want to eat something," he said. "And you know what? Nobody wants to do their jobs."
El Salvador native Sonia Contreras said the treatment of the people had nothing to do with where they were from.
"God sent them to Earth like you and me, and they have rights to be in this world," she told the cashier. "Leave the laws to the people who make the laws."
Over the course of the "What Would You Do?" experiment, 88 people came into the store. Of those, 49 didn't get involved at all and nine sided with the cashier. Thirty customers came to the defense of the day laborers.
The scene at the deli came at a time when Americans are very sensitive about losing their jobs and immigrants are concerned for their safety.
Last month, two Ecuadorian men were viciously beaten walking home from a bar in Brooklyn, N.Y. One died days later, after being taken off life support.
And in November, Ecuadorian immigrant Marcello Lucero was stabbed to death on New York's Long Island by a group of teenagers who allegedly set out that night to kill a Hispanic person. Seven teens were charged in Lucero's death.