The Justice Department indicted 11 Chinese nationals Wednesday for allegedly overseeing a decade-long scheme to arrange fraudulent marriages with U.S. citizens.

Attorney General Todd Blanche said the individuals arranged more than 1,000 sham marriages so Chinese foreigners could apply for green cards to legally remain in the United States.

“This scheme was not a quick, fly-by-night operation, but rather a yearslong, multimillion-dollar cottage industry to criminally assist people who would not, or legally could not, otherwise become citizens of the United States,” Blanche said at a news conference.

He said the operation was one of the largest marriage fraud prosecutions in U.S. history, taking in tens of millions of dollars since 2016.

The indictment alleges the Chinese nationals in some cases acted as facilitators to find U.S. citizens who were willing to participate in the sham marriages, employing attorneys, tax preparers and marriage officiants. Others were in charge of identifying foreign nationals who were willing to pay for the green cards.

He said the indicted individuals used social media advertising to market fraudulent immigration services to foreign nationals from China, who would pay as much as $100,000 to obtain a marriage, while U.S. citizens were paid up to $30,000.

The marriages were staged with fake ceremonies, including wedding attire and attendees, and documented in photos to make them appear legitimate, Blanche added, after which the couple would open joint bank and mobile phone accounts.

“After the marriages took place, the married couples would visit a local office affiliated with the scheme, sign forms for submission to the U.S. Citizenship and Immigration Services, learn about the USCIS interview process to apply for a green card and then execute prenuptial agreements, which, not surprisingly, given the allegation these were sham marriages, waives their rights to share in the other’s estate upon death, child support and other claims in marital property,” he said.

Marriage fraud is punishable with up to five years in prison and $250,000 in fines, according to Immigration and Customs Enforcement. It can also result in a green card’s revocation and deportation.

According to the Center for Immigration Studies, of the roughly 1 million green cards issued in the 2022 fiscal year, nearly a quarter went to the spouses of U.S. citizens.

According to ICE, more than 90% of marriage-based green card applications are genuine, but criminal rings and individual fake marriages are common enough that they routinely investigate them.

Last September, USCIS, which, like ICE, is part of the Department of Homeland Security, said it had discovered several instances of marriage fraud in Minneapolis.

In February, USCIS said it indicted 11 individuals for their alleged roles in marriage fraud and bribery. The indictment alleged they were Chinese nationals who recruited U.S. citizens who were members of the armed forces to enter sham marriages in New York, Connecticut, Nevada and Jacksonville, Florida.

In the indictment announced Wednesday, the DOJ said it worked with DHS, Homeland Security Investigations and the FBI.

Blanche could not say Wednesday whether anyone who received a green card through the scheme would have it revoked or be deported.

“It depends on the circumstances,” he said, adding that the DOJ is looking into thousands of marriages. “Some of them already have their green card. Some of them may actually be citizens. That’s part of the investigation that we’re doing now.”