Illinois Attorney General Kwame Raoul and Democratic attorneys general from 14 states and Washington, D.C. pushed back against the U.S. Department of Homeland Security’s proposed changes to visas for international students in a letter to Trump administration officials on Monday.

Under current rules, international students can legally remain in the U.S. as long as they maintain full-time enrollment at their institution. But DHS announced in late August that it would move to set the duration of visas to match a student’s program length and four years at most.

Students needing to extend their stay will need to apply with the United States Citizenship and Immigration Services, allowing more oversight from DHS. The new rule also makes it more difficult for international students to transfer schools or change their program.

“Welcoming international students to our colleges and universities creates a more enriching educational environment for all students,” Raoul said in a statement. “The Trump administration’s proposal would harm our institutions of higher education and our economy.”

DHS, in an August news release, said the move would explicitly help DHS reduce the number of visa holders in the U.S.

“For too long, past Administrations have allowed foreign students and other visa holders to remain in the U.S. virtually indefinitely, posing safety risks, costing untold amount of taxpayer dollars, and disadvantaging U.S. citizens,” the DHS release states.

In their letter, the Democratic attorneys general said DHS’ move violates the Administrative Procedure Act, which governs how federal agencies can propose and establish new regulations.

The attorneys general also criticized DHS for harming international students. They noted that while most undergraduate programs can be completed within four years, graduate and doctoral programs usually require more time, forcing students to deal with the complex process to obtain an extension.

The attorneys general also warned that the changes could reduce tuition revenues for colleges, ultimately harming domestic students and the U.S. economy.

“Limiting international students’ ability to study in the U.S. will only undermine the health of Illinois’ economy and result in fewer course offerings, student services, academic support and housing services for both international and American students,” Raoul said in the statement.

Since the proposed rule’s publication in August, it has drawn praise from anti-immigration groups. But education leaders and some employers have questioned the move as deterring international talent from coming to the U.S.

As of Monday — the last day of the comment period — the proposed rule has received nearly 22,000 comments. DHS is expected to publish a final version of the rule within months.