The U.S. Supreme Court on Tuesday widened the ability of states to use criminal laws against illegal immigrants and other people who do not have work authorization in the United States in a ruling involving identity theft prosecutions in Kansas.

In the decision, the justices upheld the authority of states to prosecute immigrants for identity theft when applying for a job. The court found that Kansas did not unlawfully encroach on federal authority over immigration policy in charging three men accused of using other people’s Social Security numbers.

President Donald Trump’s administration backed Kansas in the case. Trump has made his hardline policies toward immigration a centerpiece of his presidency and 2020 re-election campaign. Kansas is one of several conservative states that have sought to crack down on illegal immigrants.

The justices overturned a 2017 Kansas Supreme Court decision that had voided the convictions of the three restaurant workers, finding that a 1986 federal law called the Immigration Reform and Control Act did not prevent states from pursuing such prosecutions.

Though immigration-related employment fraud is a federal matter, Kansas contended that its prosecutions were not immigration-related and did not conflict with federal immigration law. Kansas had argued that a ruling in favor of the immigrants would undermine its ability to combat the growing problem of identity theft.

Immigrant rights groups have said that giving states power to prosecute employment fraud would let them take immigration policy into their own hands.

The three men – Ramiro Garcia, Donaldo Morales and Guadalupe Ochoa-Lara – were not authorized to work in the United States and provided their employers Social Security numbers that were not their own.

A Social Security number is used to identify people for employment and tax purposes. People who enter the country illegally do not get assigned Social Security numbers, which are given by the U.S. government to all legal residents.

The case focused on the employment verification process under federal immigration law requiring employers, on a form known as the I-9, to attest that an employee is authorized to work. The law also states that the form “may not be used for purposes other than for enforcement of this act.”

While the federal government has the sole authority to prosecute individuals for providing fraudulent information during the I-9 employment verification process, the state prosecuted the three men for using the same false information on different forms used to withhold wages for tax purposes.

(Reporting by Andrew Chung; Editing by Will Dunham)