In a major policy shift, the Homeland Security and Justice departments are promising to prosecute everyone suspected of illegally entering the United States. The new approach will separate thousands of children from their parents when they are arrested, which critics called inhumane.

“We need legality and integrity in our immigration system. That’s why the Department of Homeland Security is now referring 100 percent of illegal Southwest border crossings to the Department of Justice for prosecution,” Attorney General Jeff Sessions said at a news conference in San Diego on Monday.

“If you cross this border unlawfully, then we will prosecute you. It’s that simple. If you smuggle illegal aliens across our border, then we will prosecute you. If you are smuggling a child, then we will prosecute you and that child may be separated from you as required by law,” Sessions said as a protester with a bullhorn interrupted his remarks.

Politico reported Monday that Homeland Security Secretary Kirstjen Nielsen signed a memo on Friday directing the department to refer all suspected border crossers to the Justice Department for prosecution under a federal statute that prohibits illegal entry. Illegally entering the country has typically been treated as a civil matter in which the immigrant is subject to deportation. The new policy means all cases will be treated as a criminal matter in which immigrants face prison.

Border Patrol agents were told of the new policy over the weekend, said a federal law enforcement official who asked not to be identified because he or she wasn’t authorized to speak publicly.

“At muster they just said, ‘We are now prosecuting everyone, 100 percent.’ Then there were a few cheers and someone shouted, ‘Thank you, Trump.’ They followed up with family unit situations and said that if a unit was apprehended that the parent with the most criminal history would be prosecuted,” the official said.

One of the biggest changes in the 100 percent prosecution policy will be the separation of families accused of illegally crossing the border together. Children, who cannot be held in criminal detention, will be placed in the custody of the Department of Health and Human Services while their parents are in custody. Previously, families caught entering the country illegally were most often quickly released together to await civil deportation hearings.

The 100 percent prosecution policy “is yet another solution in search of a problem,” said Jeremy McKinney, national secretary of the American Immigration Lawyers Association. ”Illegal entries are at forty-year lows and net migration with Mexico remains at or below zero. There exists an annual, spring/summer uptick in unlawful entries. But the numbers are not unusual and the (federal immigration enforcement) infrastructure is there to enforce our country’s immigration laws. Devoting our finite resources to achieve misdemeanor convictions, especially when it results in the separation of mothers from their children, is, at best, bad public policy, and, at worst, unlawful selective prosecution.”

The Department of Homeland Security said it used a tough prosecution approach against parents in the Border Patrol’s El Paso sector between July and November 2017, after the West Texas and New Mexico border region saw a surge in families and unaccompanied children. Homeland Security said illegal crossings by family units dropped by 64 percent after the aggressive prosecution began, then began to rise again after the program was “paused.”

Andre Segura, legal director for the American Civil Liberties Union of Texas, said that is a simplistic analysis. “Crossings can vary depending on a number of factors, what’s going on in home countries—there are a lot of different factors,” he said.

The Washington Post, which first reported the plans to arrest parents who bring their children into the country illegally, said jailing parents would deter others from attempting to unlawfully enter the United States.

Sessions reinforced that message at his San Diego news conference. “I have to say our goal is to have the whole world know that this border is not open. Don’t come unlawfully. Don’t put yourself or your family through such a stressful thing,” Sessions said.

The ACLU’s Segura said immigration policy requires multiple approaches. “Immigration policies should not be set based on deterrence alone. If this is, in fact, deterring people from fleeing violence and coming here for refuge, that is an enormous problem.”

Thomas Homan, the outgoing head of Immigrations and Customs Enforcement, also spoke at the San Diego news conference and said police separate families all the time when making arrests.

“Every law enforcement agency in this country separates parents with children when they’re arrested for a crime. We are a law enforcement agency. We are enforcing the criminal laws,” Homan said. “So I want to make this perfectly clear. There is no new policy. This has always been the policy. Now, you will see more prosecutions because of the attorney general’s commitment to zero tolerance.”

Entering the United States without permission and proper documents has long been a misdemeanor, but previous policies allowed many of those apprehended to go through the administrative deportation process rather than face criminal charges.

The new policy applies to people who enter the country without permission, such as coming in at an area other than a port of entry. It would not apply to people who surrender at ports of entry to seek asylum.

Criminal prosecutions for violating immigration laws spiked during President Obama’s first term, reaching nearly 100,000 in fiscal year 2013, according to the Transactional Records Access Clearinghouse at Syracuse University. Such prosecutions declined in Obama’s second term and in President Trump’s first year in office, with fewer than 60,000 prosecutions in fiscal year 2016.

Sessions last week announced that the Justice Department was assigning 35 additional U.S. attorneys to the Southwest to handle additional immigration cases. That includes eight new prosecutors for the Southern District of Texas, which has the highest number of immigrant apprehensions along the border, and six in the Western District of Texas.

During his news conference, Sessions once again pointed to an increase in undocumented immigrant apprehensions in recent months. He said the number of apprehensions on the Southwest border tripled in April compared to the same month a year ago. However, Customs and Border Protection statistics show that the number of apprehensions over the past twelve months is 23 percent below the prior twelve-month period. Apprehension levels are less than half the levels of a decade ago.