McALLEN, Texas (AP) — The U.S. government has started requiring migrants without passports to submit to facial recognition technology to take domestic flights under a change that prompted confusion this week among immigrants and advocacy groups in Texas.

It is not clear exactly when the change took effect, but several migrants with flights out of South Texas on Tuesday told advocacy groups that they thought they were being turned away. The migrants included people who had used the government’s online appointment system to pursue their immigration cases. Advocates were also concerned about migrants who had crossed the U.S.-Mexico border illegally before being processed by Border Patrol agents and released to pursue their immigration cases.

The Transportation Security Administration told The Associated Press on Thursday that migrants without proper photo identification who want to board flights must submit to facial recognition technology to verify their identity using Department of Homeland Security records.

“If TSA cannot match their identity to DHS records, they will also be denied entry into the secure areas of the airport and will be denied boarding,” the agency said.

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Agency officials did not say when TSA made the change, only that it was recent and not in response to a specific security threat.

It’s not clear how many migrants might be affected. Some have foreign passports.

Migrants and strained communities on the U.S.-Mexico border have become increasingly dependent on airlines to get people to other cities where they have friends and family and where Border Patrol often orders them to go to proceed with their immigration claims.

Groups that work with migrants said the change caught them off guard. Migrants wondered if they might lose hundreds of dollars spent on nonrefundable tickets. After group of migrants returned to a shelter in McAllen on Tuesday, saying they were turned away at the airport, advocates exchanged messages trying to figure out what the new TSA procedures were.

“It caused a tremendous amount of distress for people,” said the Rev. Brian Strassburger, the executive director of Del Camino Jesuit Border Ministries, a group in Texas that provides humanitarian aid and advocacy for migrants.

Strassburger said that previously migrants were able to board flights with documents they had from Border Patrol.

One Ecuadorian woman traveling with her child told the AP she was able to board easily on Wednesday after allowing officers to take a photo of her at the TSA checkpoint.

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Associated Press writer Elliot Spagat in San Diego contributed to this report.