HOUSTON — President Donald Trump is standing firm on his threat of sending undocumented immigrants, who are detained along the southwest border, to "sanctuary cities" unless Congress takes action on his proposed immigration reform.

There is no legal definition of the term, which makes it difficult to track down an accurate list of the cities the president is considering.

The Texas Attorney General's Office told KHOU 11 News, "we have not issued an official definition of a 'sanctuary city.'"

The term, though, is commonly used to describe a community that doesn’t enforce federal immigration laws. In September 2017, Texas Senate Bill 4 took effect.

Dubbed the "sanctuary city bill," it makes sure that peace officers in Texas have the opportunity to ask the immigration status of a person who is detained or arrested. It also allows local cops to help federal immigration officers with enforcement, and it allows the feds to enter a city or county jail to enforce immigration laws.

SB-4 has been in a legal limbo since the day Texas Governor Greg Abbott signed it into law in May 2017.

The ACLU filed a motion to block it from taking effect. At one point, a U.S. District Judge placed an injunction on the law. But in March 2018, in spite of protests and support from some politicians, a federal appeals court ruled that most of SB-4 can remain in effect while the case plays out.

The only portion that’s currently in question is punishment for not endorsing the state law.

The Houston Police Department confirms it's complying with SB-4, giving officers discretion to ask a person’s legal status. The Harris County Sheriff’s Office confirms it does not require its employees to ask the residency of anyone detained or arrested.

But the San Antonio Police Chief is now being sued by the Texas Attorney General who is claiming the police chief violated the state’s immigration law when he turned down federal help after a dozen undocumented immigrants were found in the back of a big rig. San Antonio Police then released the undocumented immigrants. The suspected smuggler was charged with a state crime.

So while undocumented immigrants continue to be caught along the Texas/Mexico border, because of state law, if President Trump does send undocumented immigrants to "sanctuary cities," they won't be in Texas.

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