While President Obama assured that illegal immigrants granted executive amnesty would not be put on a path to citizenship, a loophole expanded by the administration has allowed just that, and two Republican lawmakers are demanding answers.

Obama’s 2012 Deferred Action for Childhood Arrivals (DACA) program grants pseudo legal status and work permits to certain illegal immigrants who came to the U.S. as children. DACA recipients are technically ineligible for permanent residency and citizenship. Due to an administrative loophole, however, DACA recipients have been able to obtain a benefit called “advance parole,” which allows a recipient to seek and obtain permanent residency and eventual citizenship.

“The grant of advance parole to DACA recipients does indeed open the door to undocumented immigrants to gain U.S. citizenship,” Senate Judiciary Committee Chairman Chuck Grassley (R-IA) and Senator Mike Lee (R-UT) wrote in a letter to Department of Homeland Security Sec. Jeh Johnson Wednesday.

“Though the federal statute governing the parole authority requires that parole be granted only for ‘urgent humanitarian reasons’ or in cases of ‘significant public benefit,’ United States Citizenship and Immigration Services (USCIS) policy has expanded potential grounds of advance parole approval for DACA recipients to ‘educational purposes, employment purposes, or humanitarian purposes,’” they explained.

The result of the expanded justifications for “advance parole” has been that DACA recipients need only travel to another country and back for reasons like studying abroad in order to have their status adjusted to parolee, a distinction that is more easily placed on a path to citizenship. According to the Senators, this loophole has been highlighted and utilized by amnesty advocates for years.

“Since 2013, the number of DACA recipients who have obtained advance parole, left the country and returned as parolees, and then adjusted to lawful permanent resident status can only have increased,” the lawmakers wrote.

In their letter, Grassley and Lee demand numbers detailing how many illegal immigrant DACA recipients have been granted parole, travelled abroad, and sought permanent residency.

“A recent story in a California newspaper describes how exploitation of this loophole has now become a cottage industry,” they wrote.

“According to the story, undocumented, DACA-recipient students at various Southern Californian universities have started going on organized ‘study abroad’ trips to Mexico after securing advance parole from USCIS, returning as parolees who are then eligible to adjust to lawful permanent resident status,” Grassley and Lee added. “One professor of Chicano Studies at Cal State Long Beach is described as having ‘discovered’ the advance parole provision in 2014 and used it to take two students to Mexico that spring. In December, 2015, that same professor used advance parole to take 30 undocumented students from across Southern California to study and visit family in Mexico. He plans to take another round of students this summer.”