Selecting San Francisco’s former police chief to head the U.S. Border Patrol would encourage more illegal border crossings because she has a record of not enforcing federal immigration laws, Sen. Ron Johnson, R-Wis., argues.

Heather Fong advocated San Francisco’s “sanctuary city” policy of non-cooperation with federal immigration officials, Johnson said in a letter Monday to U.S. Customs and Border Protection Commissioner R. Gil Kerlikowske.

“The selection of such a candidate would send a strong message—both in the U.S. and outside of the U.S.—that enforcing our immigration laws is not a priority of U.S. Customs and Border Protection,” Johnson wrote.

His letter asks Kerlikowske to answer a series of questions by Dec. 21 focused on what the agency is looking for in a Border Patrol chief. (See the entire letter here.)

As police chief, Fong upheld San Francisco’s status as a sanctuary jurisdiction, refusing to cooperate with U.S. Immigration and Customs Enforcement and protecting illegal immigrants from deportation.

Fong, 59, currently is assistant secretary of state and local law enforcement at the U.S. Department of Homeland Security, the parent agency of  the involved border and immigration agencies. She has held the post since November 2014.

Johnson, chairman of the Senate Homeland Security and Governmental Affairs Committee, said in a statement provided to The Daily Signal that he “strongly” advised against Fong’s selection and asked Customs and Border Protection to be transparent in its vetting process:

It is obvious from our committee’s 13 hearings on border security and from multiple visits that our borders are not secure. It is extremely important that whoever is appointed to lead the Border Patrol is as serious about this reality as our committee is.

A 32-year veteran of the San Francisco force, Fong served as chief from 2004 to 2009.

“We do not cooperate with ICE [Immigration and Customs Enforcement] when they go out for enforcement of immigration violations of the law,” Fong told reporters in November 2008.

Fong caught heat for sending eight crack dealers who were in the U.S. illegally to halfway houses in Southern California instead of turning them over to federal immigration authorities for imprisonment or deportation.

In a press conference three months before, Fong told reporters: “We do not work on enforcing immigration laws.”

The Border Patrol position opened up when Chief Michael Fisher announced his retirement in October.

Fox News Channel last month reported Fong’s potential consideration. That spurred Kerlikowske, the Customs and Border Protection commissioner who will appoint the new chief, to release a statement saying the agency had not yet begun a search.

“It is completely false that any individual could be a potential candidate at this time,” Kerlikowske said.

But Johnson said reports about Fong’s inclusion on the department’s short list spurred Border Patrol agents to contact his staff because they were “fearful” that her selection would prevent them from doing their jobs.

Texas Gov. Greg Abbott last month said  there would be a “revolt” in the U.S. if she takes over the Border Patrol.

“If the president brings in someone who is going to abdicate the rule of law in this country, the American people are not going to tolerate it any more,” Abbott said.