Sen. Bernie Sanders (I-Vt.) found himself at odds with some immigration reform advocates Thursday, defending his 2007 vote against a comprehensive immigration bill and telling an audience hosted by the Hispanic Chamber of Commerce that "open borders" were a threat to American jobs.

"There is a reason that Wall Street likes immigration reform," Sanders said. "What I think they’re interested in is seeing a process by which we can bring low-wage labor into this county."

Sanders, who supported the 2013 version of immigration reform, had already waded into a moral and economic fight inside the Democratic Party. The latest round began with an interview with Vox's Ezra Klein, who asked if Sanders could favor "sharply raising the level of immigration we permit, even up to a level of open borders."

The Vermont senator vehemently disagreed. "That's a Koch brothers proposal," he said. "What right-wing people in this country would love is an open-border policy. Bring in all kinds of people, work for $2 or $3 an hour, that would be great for them. I don't believe in that."

Many progressives do believe in that. They've argued for it, in the face of opposition from many labor unions. In the run-up to Sanders's appearance, Democrats who want to blunt his campaign had circulated the Vox interview and excerpts from his old statements about immigration and protectionism. When reporters were invited to ask questions, all but one asked about immigration. CNN's Dan Merica read back some of Sanders's quotes about the 2007 immigration bill and invited the senator to respond.

“My concern about the bill that I voted against,” said Sanders, “was that there was too much emphasis on bringing low-wage workers into this country. What I want to see, and what is better about the recent bill, is a pathway toward citizenship, which is absolutely essential.”

MSNBC's Alex Seitz-Wald read to Sanders from a statement by the pro-reform group FWD.us, funded and founded by some large corporations to advocate for the 2013 bill. According to FWD, Sanders had embraced -- for years, but especially in his talk with Vox -- "the totally-debunked notion that immigrants coming to the U.S. are taking jobs and hurting Americans."

Sanders disputed that. "You’ve got to be careful about defining the word, ‘immigrants,’” he said. “What they are talking about is completely opening up the border. That was the question, should we have a completely open border, so that anybody can come into the United States of America. If that were to happen, which I strongly disagree with, there is no question in my mind that that was substantially lower wages in this country.

"When you have 36 percent of Hispanic kids in this country who can’t find jobs, and you bring a lot of unskilled workers into this country, what do you think happens to that 36 percent of kids who are today unemployed? Fifty-one percent of African-American kids? I don’t think there’s any presidential candidate, none, who thinks we should open up the borders," said Sanders.

In another answer, to Huffington Post reporter Elise Foley, Sanders insisted that he could support the 2013 immigration bill without favoring the surge in visas that Wall Street wanted. "There is a great difference in saying that we welcome immigrants, that we're going to provide a path toward citizenship to those immigrants that are in this country today, and saying: Oh, we're not going to have any borders at all," said Sanders.

The senator did not further explain why open borders would suppress wages and job opportunity, while a pathway to citizenship for undocumented immigrants already in the country would not. "Some of my Republican colleagues apparently think that the solution is, I guess, to round up everybody and throw them out of the country," said Sanders, who referred several times to the story of his immigrant parents. "If suddenly, every undocumented worker in this country disappears, the economy would collapse."

Still, Sanders's economic arguments fell flat with Javier Palomarez, president and CEO of the U.S. Hispanic Chamber of Commerce, who moderated the event.

"I think he's a bit off the mark," said Palomarez. "I think he's likening allowing more immigrants coming into the country to taking American jobs. Our position is that some of these jobs [are some] that some of our young people wouldn't take. We don't see young people lining up to pluck chickens."

Palomarez, who was hosting vetting sessions with some of Sanders's rivals, said he appreciated that the senator was at least honest about his protectionism. "He didn't try to bullshit his way through the response, frankly. I appreciated that very much."