An incoming Ph.D. student at Michigan State University was detained by authorities and deported to Iran on Monday despite having a valid visa to enter the U.S., his attorneys say.

Michigan NBC affiliate WILX reported that 27-year-old Alireza Yazdani voluntarily gave up his application to enter the U.S. and was deported on Monday after six hours of detention at Detroit Metro Airport.

His attorneys told the news station they are investigating whether Yazdani was pressured into giving up his application, which they said came after a visa was issued last month following his Michigan State admission in September.

Yazdani’s attorneys added that his deportation likely will prevent him from ever entering the U.S. again. U.S. Customs and Border Protection (CBP) officials confirmed to WILX that Yazdani was not admitted to the U.S. after being deemed inadmissible, but gave no further information.

“The issuance of a visa or participation in the visa waiver program does not guarantee entry to the United States,” CBP officials told WILX. “On January 26, Alireza Yazdani Esfidajani applied for entry into the United States, and was later deemed inadmissible at which time he withdrew his application for admission into the United States. The traveler was not arrested, rather held until a return flight could be arranged to his place of departure.”

“Applicants must demonstrate they are admissible into the U.S. by overcoming all grounds of inadmissibility including health-related grounds, criminality, security reasons, public charge, labor certification, illegal entrants and immigration violations, documentation requirements, and miscellaneous grounds,” CBP added.

An official with Michigan State told the news station that the university attempted to work with Michigan’s congressional delegation to resolve the issue and is committed to welcoming international students.

“Through the Office of International Students and Scholars, the university has worked the past 24 hours with members of our Michigan congressional delegation, other federal support agencies and the student’s lawyer to help through this difficult situation,” a university spokesperson said.

“We want international students to know we value and welcome them to our campus, and we are committed to global engagement, educating international students and collaborating with partners across the world in higher education efforts,” they added.