Indiana Attorney General Curtis Hill joined the State of Indiana to a lawsuit originally filed by the Immigration Reform Law Institute (IRLI), putting the state at the center of a wider legal battle against so-called “sanctuary” jurisdictions.

Hill, who introduced Vice President Mike Pence at Thursday’s Elkhart, Indiana Trump rally, filed Monday to join the State of Indiana as a plaintiff against Gary, Indiana. The Chicago satellite city is a Democratic stronghold and passed a so-called “welcoming city” ordinance last year that prohibits their police and city officials from complying with U.S. Immigration and Customs Enforcement (ICE) detainer orders, collecting information on suspects’ immigration status, and other actions that assist immigration enforcement.

The suit was originally filed in December on behalf of American citizen plaintiffs living in Gary by IRLI, the Washington, D.C.-based law firm arm of the Federation for American Immigration Reform (FAIR), and Indiana conservative litigators the Bopp Law Firm. The complaint posits that Gary’s ordinance violates not only 8 U.S.C. § 1373 – the federal law under which jurisdictions “may not prohibit, or in any way restrict, any government entity or official from sending to, or receiving from, [federal immigration officers] information regarding the citizenship or immigration status, lawful or unlawful, of any individual – but Indiana’s own anti-sanctuary laws as well.

Indiana, like other Republican-led states, has tried to prevent the emergence of sanctuary cities since 2011 under a state law that says municipalities and universities “may not limit or restrict the enforcement of federal immigration laws to less than the full extent permitted by federal law.” Undeterred by this law, Gary and other Democratic Indiana localities like nearby East Chicago passed similar ordinances seeking to protect their illegal alien residents from deportation.

“IRLI applauds the decision by Attorney General Curtis T. Hill, Jr., to protect Hoosiers from the dangers of sanctuary cities by intervening in this case,” Dale Wilcox, executive director and general counsel of IRLI, said in a statement. “With cities like Gary insisting on putting the interests of illegal aliens above their own citizenry, we appreciate the State stepping up to the plate to protect the interests of all Hoosiers.”

The case has attracted the attention of national open-borders groups from the outset. The Georgetown University Law Center’s Institute for Constitutional Advocacy and Protection (ICAP) – led by Obama era Solicitor General Neal Katyal – and the Public Rights Project (PRP), led by Jill Habig, a fellow at George Soros’s Open Society Foundations who previously served as Sen. Kamala Harris’s (D-CA) policy director, took up Gary’s defense in February.

The groups filed a brief attempting to have IRLI’s lawsuit thrown out on the basis that Indiana’s anti-sanctuary law must be read narrowly and does not explicitly prohibit bans on “collecting” immigration information. The blanket provision banning local enforcement of immigration laws to “less than the full extent permitted by federal law” also does not preclude Gary’s ordinance, according to the brief, because Gary’s concerns over being sued under the U.S. Constitution’s Fourth Amendment justify the limitations.

“Our welcoming city ordinance is fully consistent with state and federal law, and this new filing demonstrates our commitment to fighting this lawsuit and the dangerous effort to undermine local law enforcement priorities it represents,” Gary Mayor Karen Freeman-Wilson said in March as these groups rushed to her city’s aid.

The opposing sides of the Gary lawsuit have been prominent combatants elsewhere in the fight to protect and expand sanctuary policies around the country.

On Wednesday, IRLI and the Bopp Firm followed up Hill’s decision to join their Gary Lawsuit by filing a similar lawsuit against East Chicago, another Northwest Indiana Democrat-run industrial city trying to become a sanctuary jurisdiction. That suit adds a constitutional dimension to anti-sanctuary cases, alleging U.S. Citizens in East Chicago’s rights under the Fourteenth Amendment’s Equal Protection Clause are violated by their different treatment from those facing “deportation risk.”

ICAP served as co-counsel for the Texas Democrat-run cities suing to overturn that state’s toughest-in-the-nation anti-sanctuary state. That law was upheld by the U.S. Court of Appeals for the Fifth Circuit in March. It also filed an amicus brief in Chicago’s so far successful bid to keep federal money flowing to their police despite their resistance to immigration enforcement and similar litigation in California.

All this is taking place over the backdrop of a thick web of litigation concerning sanctuary cities. The federal government is trying to secure the right to pressure sanctuary jurisdictions by withholding grants; states like Indiana are suing to use their laws to stamp out their sanctuary cities; states like California are trying to impose sanctuary policies on localitie; and, most recently, a growing number of non-sanctuary jurisdictions are suing California to invalidate the statewide sanctuary policies they say harm them.

Since President Donald Trump took office, the number of sanctuary jurisdictions in the United States has nearly doubled, transforming the once tangential issue into a central political and legal struggle. The issue at stake in Indiana – whether the kind of existing anti-sanctuary legislation can be used to prevent policies like Gary and East Chicago’s “welcoming city” ordinances – may, like the national groups involved in the litigation, play an important role in this conflict.