The Trump administration sued Texas on Wednesday over a two decade-old law that offers undocumented residents of the state the same discounted tuition as other in-state college applicants, arguing that the measure violates federal immigration law.

The lawsuit came as a surprise given that the Republican-dominated state has been more than willing to cooperate with the Trump administration on its strict approach to immigration enforcement. The case was filed in the Northern District of Texas and carried a title more familiar to legal fights over immigration during the Biden administration: United States of America v. State of Texas.

“Under federal law, schools cannot provide benefits to illegal aliens that they do not provide to U.S. citizens,” Attorney General Pam Bondi said in a statement, pledging that the Justice Department would “ensure that U.S. citizens are not treated like second-class citizens.”

How or whether Texas chooses to defend the law, the Texas Dream Act of 2001, is still uncertain. The state’s Republican governor at the time, Rick Perry, championed the law and said during his failed 2012 presidential run that those who opposed it did not “have a heart.”

The party has moved considerably to the right on immigration since then. It now falls to Texas’ hard-line conservative attorney general, Ken Paxton, to represent the state in the case, and it was not clear on Wednesday what his approach would be.

Mr. Paxton is currently locked in a fierce campaign to unseat Senator John Cornyn in the state’s Republican primary next year, based in large part on the attorney general’s aggressive enforcement of immigration laws.