A former San Francisco police chief and vocal supporter of a sanctuary cities policy is on a short list of candidates to become the new chief of the Border Patrol, according to sources.

As police chief, Heather Fong shielded illegal immigrants, including aliens who committed crimes, from deportation. In contrast, it is the job of the U.S. Border Patrol to catch and deport all illegal immigrants, including those with a criminal history.

"If they bring (a police chief) in for political purposes based on the sanctuary cities model, that politicizes the job and I think it completely undermines credibility and morale in the organization," House Committee on Homeland Security Chairman Mike McCaul, R-Texas, told Fox News.

"If you have someone who is advocating for sanctuary cities, that's the opposite side. They welcome these illegal immigrants to stay in the country. And so I think it's at cross-purpose with the mission itself."

During her five years as the chief of SFPD, Fong refused to cooperate with ICE, telling reporters in November 2008, "We do not cooperate with ICE when they go out for enforcement of immigration violations of the law."

A few months earlier, she appeared in a public service campaign telling illegal immigrants they're welcome in the city. In promoting San Francisco's sanctuary city policy on TV, radio, posters and brochures in five languages, Fong said illegal immigrants had nothing to fear under her watch. "San Francisco is committed to providing safe access to public services to our communities," she said.

In a news conference unveiling the campaign, she told reporters, "We do not work on enforcing immigration laws."