The Vermont independent senator is an outspoken liberal champion on social issues, jobs and foreign policy. He is known for his boisterous speeches on the Senate floor, his blunt style and his penchant for getting under the skin of his opponents.

But when the newly minted presidential candidate takes the stage at the National Association of Latino Elected Officials meeting in Las Vegas on Friday, he will stand before many Latino lawmakers that feel he hasn't been nearly liberal enough on the issue of immigration.

"It is not his priority," Arturo Vargas, the executive director of NALEO, said on Thursday. "I think that is one of the challenges his campaign is going to have to confront."

Sanders does have a record on immigration. He backed the 2013 immigration reform law, he has worked extensively on migrant worker rights and has spoken out, at times, about how lower wages impact immigrant families more than most.

But he helped kill a 2007 immigration push and until recently, the issue was not something Sanders addressed in his presidential stump speech. When he kicked off his campaign earlier this year on the shores of Lake Champlain in Burlington, Vermont, his 3,509 word speech did not mention immigration.

"He absolutely needs to get up to speed," Debra Guerrero, a member of the San Antonio Independent School District and NALEO attendee. "If he wants to serve as our leader ... he needs to be aware of what the future holds and immigration is a part of that."

Omar Narvaez, a NALEO member and a Dallas County Schools Board of Trustee, said "it could be a bit of a problem, especially for those of us who come from southern states or states that border Mexico."

"If you are going to run for president, you have to have some plan or thought process that you can delver for us," he said.

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The Latinos gathered Las Vegas feel that Sanders has not brought the same forcefulness he usually does to liberal causes when talking about immigration. Many attribute this to the fact he is from Vermont, a state that has fewer than 10,000 undocumented immigrants, according to Pew Research

Sanders' lack of outspokenness on immigration has caught the attention of some of his colleagues on Capitol Hill, too.

"I don't know if he likes immigrants because he doesn't seem to talk about immigrants," Rep. Luis Gutiérrez, D-Illinois told Larry King earlier this month. "But sooner or later, he'll tell us. I hope he likes immigrants. I haven't heard him say anything. He's been kind of quiet and silent."

Sanders will address the audience at NALEO on Friday and his campaign aides said this week that he will outline, in detail, his views.

In a statement to CNN, Sanders noted that, as the "son of an immigrant," he believes it is "time to bring our neighbors out of the shadows."

"It is time to give them legal status," he said. "It is time to create a reasonable and responsible path to citizenship."

Sanders pushed back against the idea that he isn't outspoken enough on immigration by noting his record of voting for immigration reform and workers' rights.

"The Republican majority in both the House and the Senate needs to let us debate and pass real immigration reform," Sanders told CNN.

Polls show Sanders struggling with minority voters.

A CNN/ORC poll released earlier this month found that 5% of non-white voters supported Sanders for president, compared to 10% of overall voters who support the independent senator.

By comparison, Hillary Clinton -- the Democratic frontrunner who won a majority of Latino voters in her 2008 primary vote against then Sen. Barack Obama -- enjoyed 62% support from non-white voters.

Vargas, the executive director of NALEO, said it wasn't too late for Sanders, however.

"Immigration is an extremely important issue, it is not the only issues," he said. "You have people here who are running school districts. What is his policy on public education? You have people here running cities. What is policy on infrastructure? And what is his policy on public safety?

"I wouldn't say he has a clean slate. But he certainly is an unknown factor and I think tomorrow is an opportunity for him to define himself," Vargas said.