The recent debate over the use and abuse of H-1B visa program has generally focused on its impact in Silicon Valley, where technology firms have brought over high numbers of skilled workers from abroad. But it may surprise people to know that as recently as 2004, it was an obscure charter school in Texas that filed for more H-1B visas than Google for that year.

Under section 101(a)(17)(H) of the Immigration and Nationality Act, this visa program was established to temporarily allow foreign workers with much needed skills in highly specialized fields of knowledge, with the intention that this program would not be abused in a way that would take away jobs from eligible American workers. But clearly this has not been the case.

Harmony Public Schools in Texas, which is part of a nationwide network of charter schools linked to the Turkish preacher Fethullah Gülen, has allegedly used this visa program to not only bring over thousands of teachers from Turkey, but also to fulfill jobs that are much less “specialized,” ranging from gym teachers to accountants to financial managers. With up to 170 Gülen-linked schools operating across the United States, they have become one of the largest sources of abuse of the program.

The issue is high on President Donald Trump’s radar. On April 18, 2017 the president signed an Executive Order directing federal agencies to propose reforms to the H-1B visa system, including the removal of fast-track approvals. But federal immigration authorities should also be keenly aware that the problem goes far beyond the IT sector.

In recent years, thousands of Turkish males have obtained H-1B visas under this network of charter schools, coming at the expense of local U.S. educators, who are supposedly unable to fill math and science (or even administrative and counseling) positions at the Gülen schools.

Locked into their position by the terms of their visa, whistleblowers tell us that many of the Turkish H-1B recipients have also been threatened with deportation unless they agree to kick back part of their salary and other earnings to the organization, a practice that constitutes human trafficking under U.S. law.

The abuse is widespread. At 59 Gülen-linked schools in the Western and Midwestern regions, 2,210 H-1B visa applications have been tallied since 2001, costing taxpayers up to $8.7 million. In Ohio alone, the Concept schools network filed 657 H-1B applications from 2001-2016, while Concept itself filed 176 H-1B applications during the same time period – during this same period state auditors found that $27.3 million of charter school funds were misspent.

Investigations have found some disturbing practices among these schools, with separate practices and protocols for their Turkish teachers. Whistleblowers have informed us that these teachers are evaluated not on the basis of their teaching skills, but on their ability to recruit new members to the movement – one school even established a points system for proselytizing promising students into extra-curricular activities with related organizations.

In Nevada, the Gülen Organization is trying to open educational institutions on U.S. military bases. The Coral Academy of Science Las Vegas (CASLV), a Gülen charter school is negotiating with our military commanders to open a school at Nellis Air Force Base north of Las Vegas, home to what is commonly referred to as “Area 51,” where some of our country’s most sensitive military technology and hardware are developed.

In addition to dozens of other locations, the network opened a school at Davis-Monthan Air Force Base in 2009, and has attempted to expand its reach into Marine Corps Base, Hawaii and Naval Station Great Lakes, Illinois. The American people should be deeply concerned about the spread of such a secretive group, which routinely and systemically denies any affiliation with their patron, and which features a record of presenting falsified documentation in its applications (as was the case in Lewiston, ME – an incident addressed at length by Mayor Robert Macdonald).

According to the recent U.S. Ambassador to Turkey James Jeffrey, Fethullah Gülen stated in a public sermon that “our friends, who have positions in legislative and administrative bodies, should learn its details and be vigilant all the time so they can transform it and be more fruitful on behalf of Islam in order to carry out a nationwide restoration.” Given how events have developed in Turkey, this charter school network – and specifically its abuses of the H-1B visa program – merits serious concern and scrutiny by the relevant authorities.

The H-1B visa program plays an important role in filling the gaps in the U.S. skilled worker program, but it should not become a cost-saving loophole or an opportunity for a foreign organization to exploit. The reforms being considered by the Trump administration are very important, and authorities should examine how Gülen charter schools have secured approvals for so many H-1B “highly skilled” worker visas over the last few years.

Robert R. Amsterdam is an international lawyer and founder of Amsterdam & Partners LLP, and acts on behalf the Republic of Turkey.