WASHINGTON — The Trump administration plans to begin turning asylum-seekers back across the southern border on Friday to wait in Mexico under a new policy designed to crack down on immigration by Central American families, according to three Department of Homeland Security officials familiar with the matter.

Customs and Border Protection officers will begin returning asylum-seekers trying to enter at the San Ysidro port of entry in California from Tijuana, Mexico, where thousands of migrants from Honduras, Guatemala and El Salvador are already waiting in poor conditions.

Under current policy, immigrants who pass an initial "credible fear" interview are allowed to remain in the U.S. while they wait for immigration judges to decide their cases. Single adults are detained while they await their hearing, but a federal court decision in 2015 mandates that families with children be detained no longer than 20 days.

An unaccompanied minor, part of a caravan of thousands from Central America, reacts as he is allowed to enter the United States to apply for asylum at the Otay Mesa port of entry on Dec. 17, 2018. Carlos Barria / Reuters

The Trump administration has blamed that court decision, known as the Flores settlement, for being a magnet that is driving record numbers of immigrant families to apply for asylum at the southern border. Last summer under the "zero tolerance" policy, DHS separated asylum-seeking parents from their children at the border, sparking international outcry.

Overall numbers of undocumented immigrants apprehended or stopped from legally entering the United States are lower than the historic highs reached in the early 2000s.

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Children who travel without a guardian, immigrants who appear ill as well as other "vulnerable populations" will be exempt from the policy and allowed to wait in the U.S. for an immigration hearing.

Immigrant and civil rights organizations have threatened to sue the Trump administration over the policy, known as Migration Protection Policy, which Homeland Security Secretary Kirstjen Nielsen announced was coming in her congressional testimony in December.

Migrants wait for food at a camp containing hundreds of Central Americans hoping to seek asylum in the U.S. on Dec. 12, 2018, in Tijuana, Mexico. Leah Millis / Reuters

The policy is a unilateral move by the U.S. and not part of an agreement with Mexico, two officials said, though Mexico has agreed to care for immigrants who are waiting to apply. The Lopez Obrador administration in Mexico has been vocal about its opposition to the policy in the past.

Beginning Friday, the asylum-seekers who come to the San Ysidro port of entry will be sent back to Tijuana with a notice to appear in court in San Diego. On their court dates, U.S. Immigration and Customs Enforcement will provide transportation from the port of entry to immigration court. Asylum-seekers will also be given a 24-hour hotline to call for the status of their asylum cases.

Shutdown has furloughed immigration court judges

Due to a backlog in U.S. immigration courts of more than 800,000 cases, asylum-seekers currently have to wait months or even years to see a judge. DHS has asked the Justice Department to expedite the cases of immigrants waiting in Mexico, and two officials said they expect the asylum-seekers affected by the new policy to wait no more than a year.

The partial government shutdown over President Donald Trump's plan for a border wall has furloughed immigration judges, however, so the backlog of cases is expected to rise.

Conditions for Central Americans waiting in Tijuana are already poor. CBP officers on the U.S. side are practicing "metering" where they let in somewhere from 40 to 100 immigrants per day. Shelters for families and children in Tijuana are overcrowded and many are struggling to meet migrants' basic needs.

They also face backlash from Tijuana residents who do not want their city overrun with Central Americans. Two boys were lured out of a camp and murdered late last year.

Human rights organizations have warned that turning back the small number of immigrants who are allowed to cross into the U.S. to claim asylum will only worsen the problem and force asylum-seekers to either wait in poor conditions or resort to dangerous routes to cross illegally.

Two children died in the custody of U.S. Border Protection in December after traveling with their parents through rough terrain in remote areas.