WASHINGTON — The Trump administration plans to expand its "Remain in Mexico" policy Friday by sending asylum-seekers who cross the border in the Tucson, Arizona, sector back into Mexico to await their court dates, according to an internal email obtained by NBC News.

The expansion would send immigrants claiming asylum in and around Tucson first to El Paso, Texas, then back into Ciudad Juarez, Mexico, according to the email.

The email was sent widely to Customs and Border Protection officials, instructing them that the Tucson sector is to "begin manifesting and processing amenable persons for MPP to be returned tomorrow morning," referring to the Migrant Protection Protocol, the official title of Remain in Mexico.

CBP is already sending asylum-seekers who are not from Mexico and are mainly from Central America back into Mexico if they cross into the El Paso and Rio Grande Valley sectors of Texas.

CBP referred NBC News to the Department of Homeland Security for comment. DHS did not immediately respond to a request for comment.

In October, 6,352 undocumented immigrants crossed into the Tucson sector, a 262-mile stretch of border between the New Mexico state line and the eastern edge of Arizona's Yuma County, though how many claimed asylum is unknown. Tucson was second in migrant crossings only to the Rio Grande Valley sector, which had nearly 10,000 last month.

Since Remain in Mexico went into effect in January, immigration lawyers have challenged the policy in court, claiming that asylum-seekers are having their rights violated by being made to wait in unsafe conditions in northern Mexico.

Immigrants are brought to courtrooms set up in tents on the U.S. side of the border and are facing yearlong wait times for a final adjudication of their case.

Despite court challenges, the policy remains in place.

The Trump administration unveiled another policy limiting the rights of asylum-seekers this week. Beginning Wednesday, DHS began deporting Central Americans to countries that have entered into agreements with the United States. For example, if migrants from El Salvador or Honduras pass through Guatemala on their way to the United States without claiming asylum, they would be deported to Guatemala.