Texas Attorney General Ken Paxton on Monday asked the U.S. Supreme Court to overturn a California law that forbids California state employees from taking taxpayer-funded business trips to expos or conferences in Texas.

California adopted the sanctions in response to a 2017 Texas law allowing foster care and adoption agencies to deny services based on religious beliefs. Opponents decried the law for giving the child-placement agencies legal cover to discriminate against LGBT people and others.

Supporters said the law does not have a discriminatory effect because it requires the child placement agencies, upon refusal to work with a family, to make referrals to other organizations.

Paxton, in a statement Monday, called California’s ban “economic warfare” and an attempt “to punish Texans for respecting the right of conscience for foster care and adoption providers.”

“The law California opposes does not prevent anyone from contributing to child welfare,” Paxton said. “Boycotting states based on nothing more than political disagreement breaks down the ability of states to serve as laboratories of democracy while still working together as one nation — the very thing our Constitution intended to prevent.”

A case generally has to escalate from lower courts before it reaches the Supreme Court, but the high court has exclusive jurisdiction over civil disputes between two or more states.

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California lawmakers passed the ban on state-funded travel in a law, which became effective at the start of 2017.

California Attorney General Xavier Becerra did not immediately respond to a request for comment. But in mid-2017, when adding Texas to the list of restricted-travel states, he said it was because California will not tolerate discrimination. The ban affects 11 states, including Alabama, Iowa, Kansas, Kentucky and South Carolina; one of the states, Oklahoma, has imposed a retaliatory ban on California.

“Discriminatory laws in any part of our country send all of us several steps back,” Becerra said. “That's why when California said we would not tolerate discrimination against LGBTQ members of our community, we meant it.”

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The action Monday marks the latest battle between the largely liberal California and the red state of Texas in a long-running feud, which has lately been playing out not just in the political arena but more and more in federal court. Texas is leading the multi-state suit seeking to strike down the Affordable Care Act, for example, while California leads a coalition of states defending the ACA.

The two states are on opposite ends of lawsuits that will determine the future of the Deferred Action for Childhood Arrivals program, which allows children of undocumented immigrants reprieve from deportation while they study and work.

The Texas v. California legal clashes also underline the increasing influence of politics on the types of cases that the attorney general decides to pursue.

Religious liberty has become one of Paxton’s passion issues throughout his tenure. Just within the past year, he has sued the city of San Antonio for rejecting Chick-fil-A from its airport because of company leadership’s anti-gay marriage views. And Paxton has said he will not defend a state agency being sued for punishing a Waco judge who won’t officiate same-sex marriages because of her religious beliefs.

Ricardo Martinez, CEO of Equality Texas, said the California travel ban is just one example of the economic effects that discriminatory legislation can have. He added that Texas foster children have slept in state offices for years in part because of a lack of placements.

Paxton’s “religious liberty excuses are a false argument to continue his clear and ongoing war on LGBTQ Texans, as evidenced by the dozens of actions he has taken against our community while in office,” Martinez said.