A group of 15 Chinese nationals are accused of orchestrating a vast conspiracy to help foreign students cheat on standardized college entrance exams administered in the U.S., in what appears to be one of the more brazen testing-related scandals in the past decade, according to a federal grand jury indictment unsealed Thursday.

For the past four years, the defendants provided counterfeit Chinese passports to impostors, who then sneaked into testing centers, mostly in western Pennsylvania, where they took the Scholastic Aptitude Test (SAT), the Graduate Record Examination (GRE), or the Test of English as a Foreign Language (TOEFL), while claiming to be someone else, according to the indictment.

It’s unclear how many students used these fraudulent test scores to gain admission to American colleges and universities, and to therefore illegally obtain F1 Student Visas.

“These students were not only cheating their way into the university, they were also cheating their way through our nation’s immigration system,” said special agent John Kelleghan of Homeland Security Investigations in Philadelphia. “HSI will continue to protect our nation’s borders and work with our federal law enforcement partners to seek out those committing transnational crimes and bring them to justice.”

A federal grand jury in Pittsburgh issued an indictment on May 21 on 35 charges, including conspiracy, counterfeiting foreign passports, and defrauding the Educational Testing Services (ETS) and the College Board, according to U.S. Attorney David J. Hickton for the Western District of Pennsylvania.

If the defendants are found guilty, they face a maximum total sentence of 20 years in prison and hundreds of thousands of dollars in fines.

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Write to Haley Sweetland Edwards at haley.edwards@time.com.