Illegal immigrants who come to the United States' southern border are figuring out how to work the U.S. immigration system by claiming asylum, Rep. Henry Cuellar said in a new interview.

During an appearance on "Full Measure" with Sharyl Attkisson slated to air Sunday, the Texas Democrat said things need to change.

"I think what's happening now is people are realizing all you have to do is get to the southern border and just claim asylum, refugee or credible fear, then they'll process you, give you the notice to appear and then you wait three, four years for a court hearing and that's why you got Haitians, you got other people," Cuellar said.

Attkisson cited figures that show more than 408,000 people entered the U.S. illegally though Mexico in fiscal year 2016, a number that includes more than 59,000 children. Five thousand Haitians came from Mexico to California, while several thousand came from Central American countries.

What's more, there was an increase in Pakistanis entering the U.S. from Mexico this year — more than 300, up from 31 in 2015.

That uptick has stoked fears of terrorism in the U.S.

"It is because people from different parts of the world — Africa, the Middle East, other parts of the world — are now realizing that all you have to do is get to the southern border of the United States and there's a process there," Cuellar said. "You can claim a legal defense and you just get to come in. I mean, people, the smuggling organizations know exactly what they're doing."

A new book written by a CIA contractor claims terrorists plan to take advantage of America's immigration laws to fill the U.S. with Muslims and then "defeat America."

President-elect Donald Trump has promised to crack down on illegal immigration when he takes office in January. Immigration advocates are now urging President Barack Obama to release thousands of Central Americans who are seeking asylum before he leaves the White House.