Members of a secretive Turkish Islamic movement that is at the center of a congressional ethics committee investigation have donated hundreds of thousands of dollars to Hillary Clinton’s presidential campaign and to her family’s charity, a Daily Caller investigation has found.

The largest donation from a leader of the Gulen movement, which is operated from Pennsylvania’s Pocono Mountains by a moderate Muslim cleric named Fethullah Gulen, came from Recep Ozkan. (RELATED: Here’s A Map Of Radical Mosques In The U.S. [Interactive])

A former president of the Gulen-linked Turkish Cultural Center, Ozkan gave between $500,001 and $1,000,000 to the Clinton Foundation in recent months, the charity’s website shows. He also served as a national finance co-chair last year for a pro-Clinton political action committee called Ready PAC.

According to Portland State University political science professor Birol Yesilada, who has studied the Gulen movement for more than 25 years, Ozkan is the New York liaison for the 74-year-old Gulen, who has lived in the Poconos since 1999 when he went into exile after he was accused of attempting to undermine Turkey’s secular regime in order to institute an Islamic state.

Gulen also recently ran afoul of Turkey’s president, Recip Tayyip Erdogan. Erdogan accused Gulenists of operating a “parallel state,” and he reportedly lobbied President Obama last month to extradite Gulen back to Turkey.

By most accounts, the Gulen movement, or Hizmet as it is known to some, is not a radical Islamic movement. Yesilada, who serves as the contemporary Turkish Studies endowed chair at Portland State University, told TheDC in an interview that he has found no evidence of Gulenist ties to any terrorist groups.

But with an estimated 8 million followers and $50 billion in assets, Gulenists do hope to influence both the U.S. and Turkish political system through a worldwide network of businesses, nonprofit organizations, media companies and charter schools, Yesilada and others familiar with the group have claimed.

To help support its diverse interests, Gulen movement supporters in the U.S. have in recent years begun to donate heavily to numerous political campaigns. Gulenists have also paid for hundreds of Turkish “cultural” trips for members of Congress from both sides of the political aisle.

Gulenists’ contributions to congressional campaigns have been known for some time, as Buzzfeed reported last year. Texas Reps. [crscore]Sheila Jackson-Lee[/crscore] and [crscore]Henry Cuellar[/crscore], both Democrats, are among the biggest benefactors of Gulen contributions.

USA Today reported last month that the House ethics committee has investigated more than 200 trips taken by members of Congress since 2008 that were secretly funded by Gulen groups.

While the ethics committee found that none of the members of Congress who went on the trips violated federal regulations, investigators found evidence suggesting that the Gulenists “may have affirmatively lied to and/or withheld information” about the junkets and falsified disclosures provided to Congress.

The matter has since been referred to the Department of Justice. The FBI has also reportedly investigated whether the Gulen movement’s charter schools — of which there are more than 130 — have taken advantage of the H1-B visa system by hiring Turkish teachers who are kicking back some of their government-paid salaries to the Gulen movement.

Some of the Gulenist campaign donations may have been illegal as well, USA Today reported on Friday. The newspaper reported that New Hampshire Sen. [crscore]Kelly Ayotte[/crscore], a Republican, returned $43,100 in donations she received from 19 Turkish donors with ties to Gulen that she received on April 30, 2014.

Many of those donors who gave to Ayotte could not be located, USA Today reported. Others gave donations that comprised a suspiciously large percentage of their incomes.

In giving back the donations, Ayotte called on other politicians, including Clinton, to return Gulen money. The Clinton campaign did not respond to an email from TheDC asking whether the Democrat would return the contributions.

Clinton has been the biggest recipient of Gulenist donations of any presidential candidate this cycle, federal election records show.

Besides his massive Clinton Foundation donation, Recep Ozkan, who is listed on various campaign finance disclosures as an executive at JIG Corp., Everglobe Partners, and Baharu Inc., gave $25,000 to the pro-Clinton Ready PAC in 2014. He contributed an additional $5,400 to her campaign this year.

As president of the Turkish Cultural Center, Ozkan hosted Clinton at Ramadan celebration dinners in 2006 and 2007 when she was in the Senate.

A photo taken during Clinton’s 2006 appearance shows her posing with Ozkan in front of a banner listing a number of Gulen-affiliated organizations, such as Zaman International Newspaper, the Interfaith Dialogue Center, and two New York-based Gulen charter schools, Brooklyn Amity School and Long Island Amity School.

Another national finance co-chair of the pro-Clinton Ready PAC is Gokhan Ozkok. A founding board member of the Turkish Cultural Center, Ozkok is listed on that organization’s website as a member of the Clinton Global Initiative. He’s also donated between $25,001 and $50,000 to the Clinton Foundation.

In addition, Ozkok, who is listed on campaign finance records as working for Gulen charter school companies like Sema Education and Apple Education Services, contributed $10,000 to Ready PAC last year and $1,500 Hill PAC in 2008. He’s given $2,700 to her formal campaign this year, and gave $5,525 to other Clinton PACs and to her presidential campaign from 2006 to 2008, records show.

A number of officials from other charities in the Gulen network such as the Turkic American Business Network, Istanbul Center, Rumi Forum, the Turkish American Business Council, the Peace Islands Institue, and the Turkic American Alliance have also donated to Clinton’s campaigns and PACs.

Altan Kalayci, the president of the Istanbul Center, which is also known as the Global Spectrum Foundation, gave $17,000 to Ready PAC in 2014, a contribution which also won him the designation of a national finance co-chair for the committee. As USA Today found in its investigation of the congressional trips, the Istanbul Center sponsored a nine-day visit to Turkey for Alabama Rep. [crscore]Mo Brooks[/crscore], his wife and four staffers which was secretly funded by a Turkey-based organization tied to Gulen.

Ercan Keskin, a board member of the Rumi Forum and the Turkish American Business Council, donated the federal maximum of $2,700 to Clinton’s formal campaign in April 2015. He gave $1,000 to her 2008 presidential campaign.

Fazli Celik, the chairman of the Rumi Forum, also gave Clinton $2,700 in April and $1,000 to her last White House bid. Zafer Akin, an attorney and president of the Peace Islands Institute, another Gulenist outfit, also gave $2,700 to Clinton’s campaign in April.

Talha Sarac, who chairs the Gulen-linked Turkish American Business Network, gave the maximum $2,700 to Clinton’s campaign on April 29, 2015, the same day that many other Gulenists gave to the Democrat’s cause. Another group executive, Emin Halac, donated the same amount to the Clinton campaign that day. Mahmut Yeter, a member of the Turkish American Business Network and former executive director of the Turkic American Associations, gave $5,050 in 2008 cycle.

Another Clinton donor operating in the Gulen network is Burak Yeneroglu, a businessman who is closely affiliated with the Turkic American Alliance. (RELATED: Major Hillary Donor Conducted Review Of Erroneous Clinton Foundation Tax Returns)

Records show that he gave the Clinton campaign $2,700 in April and donated $12,500 to her PAC last year. In 2008, he gave $5,000 to Hill PAC, the political action committee set up for Clinton in 2008.

Yeneroglu is also named in the House Office of Congressional Ethics report on trips to Turkey provided to members of Congress by Gulen organizations for a $6,100 check he wrote to the Council of Turkic American Associations in May 2013 to pay for a trip to Turkey for New Jersey Rep. [crscore]Leonard Lance[/crscore], a Republican.

None of the Gulen-linked groups asked by TheDC for comment responded. Ozkan also did not reply to an emailed request for comment.

It is not exactly clear why Gulenists have donated so heavily to Clinton’s campaign. A Clinton White House is unlikely to benefit the charter school industry which is central to the Gulenist network. In a speech earlier this month Clinton criticized charter schools, claiming that they often refuse to take students who are difficult to teach. Though Clinton and her husband have both praised charter schools in the past, the Democrat’s flip-flop was seen by many as a political appeal to teachers unions.

Asked whether the purpose of the Gulenists’ political contributions is part of an effort to support their charter schools, to open up business opportunities for Turks, or to protect Fethullah Gulen, Yesilada said “all of the above.”

“And also finding sympathetic ears for their existence,” he added, noting the annual cultural trips Gulenists provide to members of Congress.

“Gulenists right now are keeping a low profile, but they are reaching out everywhere through a very clever lobbying effort to maintain their political connections and to make sure sympathy stays,” Yesilada said.

Follow Chuck on Twitter