A July 2015 interview (at 5:54) was:
Ezra Klein: You said being a democratic socialist means a more international view. I think if you take global poverty that seriously, it leads you to conclusions that in the US are considered out of political bounds. Things like sharply raising the level of immigration we permit, even up to a level of open borders. About sharply increasing ...
Bernie Sanders: Open borders? No, that's a Koch brothers proposal.
Ezra Klein: Really?
Bernie Sanders: Of course. That's a right-wing proposal, which says essentially there is no United States. ...
Ezra Klein: But it would make ...
Bernie Sanders: Excuse me ...
Ezra Klein: It would make a lot of global poor richer, wouldn't it?
Bernie Sanders: It would make everybody in America poorer —you're doing away with the concept of a nation state, and I don't think there's any country in the world that believes in that. If you believe in a nation state or in a country called the United States or UK or Denmark or any other country, you have an obligation in my view to do everything we can to help poor people. 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. I think we have to raise wages in this country, I think we have to do everything we can to create millions of jobs.
You know what youth unemployment is in the United States of America today? If you're a white high school graduate, it's 33 percent, Hispanic 36 percent, African American 51 percent. You think we should open the borders and bring in a lot of low-wage workers, or do you think maybe we should try to get jobs for those kids?
I think from a moral responsibility we've got to work with the rest of the industrialized world to address the problems of international poverty, but you don't do that by making people in this country even poorer.
07 June 2007 Bernie Sanders said:
I must oppose bringing in hundreds of thousands more workers into the United States who would lower wages and hurt American workers
Also Sander's official senate website still says:
Sanders had argued that helping unemployed American young people was the least Congress should do in a bill that allows college students from around the world to take jobs that young Americans would otherwise perform.