The passenger added that the couple did not immediately hear the comment, which prompted the man to repeat his remark.
KHOU reported that a woman sitting nearby alerted a flight attendant, which led other passengers to also complain about the man's questions. When the Indian American boyfriend of the woman who alerted the attendant complained, a heated exchange followed.
"The person ahead of us turned around and asked where my boyfriend was from; my boyfriend said it's none of your business," the woman told KHOU. "At that point he said all illegals and all foreigners need to leave the country."
Cellphone footage of the incident shows the man saying all the "illegals" need to kicked off the plane, moments before the man and woman are asked to collect their belongings and exit the aircraft.
"I didn't say anything," the man protested, shrugging.
"Happy flight home," he added seconds later while his female companion holds her middle finger up to the person filming. "I hope you stay there."
"Get out of here," a woman responded. "Racists aren't welcome in America! This is not Trump's America!"
"Goooodbyeee raaacists!" the woman added.
"Hey, I'll come back, but you'll be gone," the man said as he walked away.
Jonathan Guerin, a United Airlines spokesman, told The Washington Post the man and woman understood why they were asked to leave the plane and calm down.
They were placed on a later flight bound for Houston, but Guerin said he didn't know if the Texas city was their final destination.
"We removed two passengers for making others feel uncomfortable on the flight and for saying some inappropriate things to customers on the flight," Guerin said, noting that removing customers from flights because of disruptive behavior is exceedingly rare.
"Most customers appreciate a place where they feel safe and where they're not going to be attacked and we want to provide that," he added.