Elected representatives who threaten to defy a future mass deportation effort would be committing felonies under US law if they obstruct federal officials, Donald Trump's border czar nominee, Tom Homan, warned.

Asked about elected reps who may defy Immigrations and Customs Enforcement officials this week, Homan said feds are coming for criminal illegals whether they like it or not.

"Well first of all, if they don't want to help us, get the hell out of the way, we're going to do it," Homan told Fox News' Lawrence Jones.

"If I got to send twice the amount of resources to that city, that's what we are going to do. If they give us access to the jail, that'll mean less agents in their community," Homan said. "For them pushing back and not letting us in the jail, it just means more agents are going to be in the community, so they're hurting themselves."

"Finally, I'll say this they need to educate themselves. They need to review this Title 8, United States Code 1324 (iii) – read about that and don't cross that line, because it is a felony to harbor and conceal an illegal alien from ICE. Read this statute. Don't cross that line," he warned.

He went on to outline his agenda items, saying Trump plans to "focus on public security threats and national security threats first, and fugitives – those who cross the border illegally, had great due process at great taxpayer expense and were ordered removed by an immigration judge and didn't leave – they're also a priority."

"And third rail, we've got to find over 300,000 missing children that were released into this country to so-called sponsors that the government can't find," he added.

Homan also expressed bewilderment to threats from Democrat Boston Mayor Michelle Wu who claimed she'll shield illegals, saying, "She's not very smart. I'll give her that."

"What I just said is President Trump is going to prioritize public safety threats. What mayor or governor doesn't want public safety threats out of their communities?"

"I mean that's your number one responsibility is to protect your communities. And that's exactly what we're going to do. So either she helps us, or she gets the hell out of the way, cause we're going to do it."