Texas Gov. Greg Abbott (R) signed into law a controversial immigration bill on Sunday.

The law, known as S.B. 4, started as a ban on "sanctuary cities" in Texas but grew in scope through amendments.

Here are five things you need to know about S.B. 4:

It forces local jails to comply with ICE detainers

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Originally envisioned as a ban on sanctuary cities — municipalities that refuse cooperation with federal authorities on certain areas of immigration enforcement — S.B. 4's main goal is to force local law enforcement to comply with Immigration and Customs Enforcement (ICE) detainers.

Detainers are requests by ICE for local police or jails to hold foreign detainees and prisoners for up to 48 hours so federal agents can pick them up and start deportation proceedings.

ICE detainers are at the core of the debate on sanctuary cities.

Many local governments say they erode trust between immigrant communities and local law enforcement and put cities at risk of liability for violation of detainee's constitutional rights.

The Trump administration says detainers help ICE keep dangerous criminals off the streets.

It punishes police departments that don't enforce it

S.B. 4 makes it a Class A misdemeanor for local law enforcement agencies to not comply with federal detainers.

Police chiefs, sheriffs, jail administrators and constables could be fined, made liable for civil action or removed from office if they don't honor detainers or if they enact department-wide policies prohibiting officers from asking individuals about their immigration status.

"Unlike [Arizona's S.B.] 1070, it doesn't focus on individual officer behavior," said Mark Jones, the Joseph D. Jamail Chair in Latin American Studies at Rice University in Houston.

That means individual police officers in Texas can choose to ask for documentation in civilian encounters ranging from felony arrests to innocuous situations such as traffic violations.

"We shouldn't expect large numbers of officers to begin asking about that," said Jones.

Many Texas police chiefs, like Houston's Art Acevedo, have come out strongly against detainers. The influence of police chiefs on their departments makes it unlikely that individual officers would risk their careers by developing a reputation for checking the immigration status of individuals they come across, according to Jones.

It's not a "show me your papers" law

Unlike Arizona's S.B. 1070, passed in 2010, Texas’ law does not compel police officers to ask individuals about their immigration status.

Although the Texas law stops police departments from banning officers from asking for proof of legal status, it doesn't include a mandate to compel officers to do so.

"Here they are saying you can't have across-the-board policies that prohibit employees from doing A, B and C, [but] there are not many areas of the law that mandate officers to do X, Y and Z," said Anne Chandler, executive director of the Tahirih Justice Center in Houston, an advocacy group that provides support to immigrant women fleeing violence.

That distinction means many police departments will continue to operate as they have previously in encounters with immigrants, according to Chandler.

Still, Democrats were quick to label the law as a full "show me your papers" initiative.

"Local police and campus police aim to protect and build trust with local residents, but the 'Show Me Your Papers' bill shifts the focus away from keeping communities safe," Rep. Filemon Vela (D-Texas) said in a statement.

This provision was first "watered down" in the Texas House, but then reinserted by conservative Republicans in the House floor during debate, said Jones.

"There was a big dispute within the Democratic caucus," said Jones. "Moderates wanted to work with GOP leadership … to allow passage but keep the more strident aspects out."

But a "core group of Democrats decided it was better" to let the amendment through, although it was the most controversial part of the law, rather than "letting legislation pass without as much opposition," he added.

It will be challenged in the courts

Despite the lack of a "show me your papers" mandate, opponents will challenge the law's constitutionality.

"I'm sure there'll be immediate challenge and probably an injunction," said Jones.

When Arizona passed its "show me your papers" law, it was almost immediately de-fanged by the courts, and eventually only parts of the law were enforced after prolonged litigation and negotiation between the state government and immigrant rights advocates.

Democrats and activists view the Texas law as an opportunity to fight not only in the Lone Star State, but also as a way to take on the Trump administration on immigration policy.

"While Governor Abbott and President Trump try to silence the Latino community, we will stand up, speak out, and march to defend our values and the rights of the most vulnerable in our country," said Democratic National Committee Chairman Tom Perez.

It's a political risk for Texas Republicans

Democrats are eager for an electoral win and will try to use controversy over S.B. 4 as a way to get Latinos in Texas to the ballot box.

Although the Texas law isn't as hard-line as previous state immigration laws, the perception of being anti-immigrant will be hard to counter for Republicans, said Chuck Rocha, a Democratic political consultant from Texas.

But Latinos, who make up about 25 percent of the Texas electorate, have been more willing to vote Republican than in other states. Abbot received more than 40 percent of the Latino vote in the state.

Jones said it will be hard to get Hispanic voters to turn on the GOP "as long as Republicans avoid rhetoric that is seen as racist."

"The impact is in the perception," said Chandler.

"The immigrant community is interpreting both the changing federal landscape and coverage in the media of the local law as one where we're living in a new reality where police are playing double duty as immigration officials," she said.

Despite the bill's nuanced approach, Democrats are already gearing up to portray it as anti-immigrant in the lead up to 2018.

"I've spent my career showing Latinos the difference between Republicans and Democrats and this couldn't be more clear," said Rocha.

"All we have to say is they signed this bill that singles us out and it allows for children to be stopped to show their papers."

For Republicans, S.B. 4 was a way for Abbott and the legislature "to throw a bone" to conservatives ahead of Republican primaries, said Jones.

Texas Lt. Gov. Dan Patrick (R) played a key role in passing the legislation, forcing Abbott's hand in supporting it.

"It's not clear if Patrick would mount a challenge against Abbott, but Abbott is not going to provide the context where that could even become a hypothetical," said Jones.