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A new system, CMS Administrator Seema Verma and other senior CMS officials announced Tuesday, will require states to conduct crosschecks on all Medicaid and Children’s Health Insurance Program (CHIP) enrollees to ensure that illegal immigrants don’t receive public coverage.

The system will work by automatically cross-checking Medicaid and CHIP enrollment records against immigration and citizenship databases to detect whether immigrants are eligible for coverage. The enrollment data checks will occur monthly, and CMS officials said in an interview that they represent one of the single largest changes to how the agency is fighting illegal immigration in the Trump administration’s second term.

“CMS is increasing oversight of eligibility verification and maintaining accurate records to ensure that taxpayer dollars are spent wisely and programs are limited to those who are lawfully eligible,” a CMS spokesperson said. “States will conduct regular monthly eligibility reviews for Medicaid and CHIP to prevent illegal immigrants from enrolling and will use automated tools to help in this process.”

States will also be required to notify CMS when any Medicaid or CHIP enrollee is found to be unlawfully present and to de-enroll them, according to agency officials. State Medicaid programs have already long been able to verify information with federal agencies, but have not been required to do so in a systematic way until now.

States must report to CMS on the cases it has flagged for immigration or citizenship status review each month. CMS will receive reports on more than 65 million Medicaid and CHIP enrollees over the coming months, according to Verma. The reports, which began arriving on Tuesday, will send red flags to CMS when a state’s enrollment rolls contain people who aren’t authorized to receive coverage.

CMS will match enrollment data against a host of databases, according to officials. They said the Social Security Administration’s database and the Department of Homeland Security’s Systematic Alien Verification for Entitlements (SAVE) system will be two of the most important federal data sources for states to check for eligibility purposes.

HHS Secretary Robert F. Kennedy Jr. said in a statement announcing the system that the administration was increasing scrutiny of immigrants in public health programs to ensure that illegal immigrants are “paying their fair share and not putting additional strain on the health care system.”

Agency Administrator Dr. Mehmet Oz added that restricting the program to legal residents was a major step to cut down on waste in health safety-net programs. “Illegal immigration places a significant financial and administrative burden on Medicaid and CHIP and saps funding that could be used to help others who are in need and are eligible for these programs,” Oz said in a statement.

CMS didn’t provide an estimate on the number of people it expected the program to catch when asked. Since the beginning of Trump’s second term, his administration has made immigration policy and strict program enrollment a top priority, with a particular focus on keeping illegal immigrants from receiving taxpayer-funded benefits.

President Donald Trump himself signed an executive order in February that began the initiative. The order called for a sweeping review of all federal benefits programs to determine how non-citizens could receive public benefits. The move was a direct rebuke to the Personal Responsibility and Work Opportunity Reconciliation Act of 1996, which a federal appeals court recently determined limited benefits for undocumented immigrants.

Months later, the HHS Secretary expanded which federal programs could be considered public benefits. Programs covered under the new rule grew by nearly a third, according to the new guidance. As a result of the HHS rule change, Medicaid was not the only government program to be placed under review as part of the White House order in February.

The announcement comes as other Republican initiatives tied to the federal benefits program are taking effect. New statutory requirements that states conduct eligibility reviews on Medicaid coverage twice a year were built into a major spending package Republicans and Democrats agreed to last month. The eligibility reviews will be expanded to all Medicaid enrollees, rather than subsets of recipients, as was the prior policy.

Democrats in a group of more than two dozen attorneys general are also suing the administration over the change. New York Attorney General Letitia James, the head of the Democratic attorneys general coalition, said that requiring states to perform verification for federally funded public benefit programs risked millions of state residents’ access to public services.

“This isn’t an abstract issue,” James said last month. “It’s a direct assault on New Yorkers and their health care, on their children’s education, on their nutrition assistance, on their workers’ rights and safety nets, on families struggling to keep a roof over their heads, and on much more.”

The lawsuit marks just one front in a long-running conflict between the federal government and Democratic-led states over public health programs and immigration status verification. Republican leaders in Congress and Washington, D.C., have taken steps to ensure that illegal immigrants don’t receive coverage, while Democrats have argued that immigrant verification is an unnecessary burden for state Medicaid programs.

CMS Administrator Dr. Mehmet Oz said that tighter eligibility rules and strict enrollment criteria were critical to safeguard taxpayer dollars. “Every dollar misspent is a dollar taken away from an eligible, vulnerable individual in need of Medicaid and CHIP,” he said.